[FEA] Support passing scalar string args to string_udfs

Using the newly merged strings_udf support, I'm trying to pass scalar arguments to a string UDF:
```
import cudf

df = cudf.DataFrame({"str_col": ["a", "abb", "abc"]})

def delim_count(row, delim):
return row["str_col"].count(delim)

df.apply(delim_count, args=("b",), axis=1)
```

But I get udf compilation failed errors.

Trace:
```
---------------------------------------------------------------------------
NumbaNotImplementedError Traceback (most recent call last)
/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/base.py in cast(self, builder, val, fromty, toty)
711 try:
--> 712 impl = self._casts.find((fromty, toty))
713 return impl(self, builder, fromty, toty, val)

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/base.py in find(self, sig)
48 if out is None:
---> 49 out = self._find(sig)
50 self._cache[sig] = out

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/base.py in _find(self, sig)
57 else:
---> 58 raise errors.NumbaNotImplementedError(f'{self}, {sig}')
59

NumbaNotImplementedError: , (unicode_type, string_view)

During handling of the above exception, another exception occurred:

NumbaNotImplementedError Traceback (most recent call last)
/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/base.py in cast(self, builder, val, fromty, toty)
712 impl = self._casts.find((fromty, toty))
--> 713 return impl(self, builder, fromty, toty, val)
714 except errors.NumbaNotImplementedError:

/opt/conda/envs/rapids/lib/python3.9/site-packages/cudf/core/udf/masked_lowering.py in cast_primitive_to_masked(context, builder, fromty, toty, val)
336 def cast_primitive_to_masked(context, builder, fromty, toty, val):
--> 337 casted = context.cast(builder, val, fromty, toty.value_type)
338 ext = cgutils.create_struct_proxy(toty)(context, builder)

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/base.py in cast(self, builder, val, fromty, toty)
714 except errors.NumbaNotImplementedError:
--> 715 raise errors.NumbaNotImplementedError(
716 "Cannot cast %s to %s: %s" % (fromty, toty, val))

NumbaNotImplementedError: Cannot cast unicode_type to string_view: %"inserted.parent" = insertvalue {i8*, i64, i32, i32, i64, i8*, i8*} %"inserted.meminfo", i8* %"arg.delim.6", 6

During handling of the above exception, another exception occurred:

NumbaNotImplementedError Traceback (most recent call last)
/opt/conda/envs/rapids/lib/python3.9/site-packages/cudf/core/indexed_frame.py in _apply(self, func, kernel_getter, *args, **kwargs)
1817 try:
-> 1818 kernel, retty = _compile_or_get(
1819 self, func, args, kernel_getter=kernel_getter

/opt/conda/envs/rapids/lib/python3.9/contextlib.py in inner(*args, **kwds)
78 with self._recreate_cm():
---> 79 return func(*args, **kwds)
80 return inner

/opt/conda/envs/rapids/lib/python3.9/site-packages/cudf/core/udf/utils.py in _compile_or_get(frame, func, args, kernel_getter)
214
--> 215 kernel, scalar_return_type = kernel_getter(frame, func, args)
216 np_return_type = numpy_support.as_dtype(scalar_return_type)

/opt/conda/envs/rapids/lib/python3.9/site-packages/cudf/core/udf/row_function.py in _get_row_kernel(frame, func, args)
132 )
--> 133 scalar_return_type = _get_udf_return_type(row_type, func, args)
134 # this is the signature for the final full kernel compilation

/opt/conda/envs/rapids/lib/python3.9/contextlib.py in inner(*args, **kwds)
78 with self._recreate_cm():
---> 79 return func(*args, **kwds)
80 return inner

/opt/conda/envs/rapids/lib/python3.9/site-packages/cudf/core/udf/utils.py in _get_udf_return_type(argty, func, args)
55 # needed here.
---> 56 ptx, output_type = cudautils.compile_udf(func, compile_sig)
57 if not isinstance(output_type, MaskedType):

/opt/conda/envs/rapids/lib/python3.9/site-packages/cudf/utils/cudautils.py in compile_udf(udf, type_signature)
249 # compilation with Numba
--> 250 ptx_code, return_type = cuda.compile_ptx_for_current_device(
251 udf, type_signature, device=True

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/cuda/compiler.py in compile_ptx_for_current_device(pyfunc, args, debug, lineinfo, device, fastmath, opt)
289 cc = get_current_device().compute_capability
--> 290 return compile_ptx(pyfunc, args, debug=debug, lineinfo=lineinfo,
291 device=device, fastmath=fastmath, cc=cc, opt=True)

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/compiler_lock.py in _acquire_compile_lock(*args, **kwargs)
34 with self:
---> 35 return func(*args, **kwargs)
36 return _acquire_compile_lock

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/cuda/compiler.py in compile_ptx(pyfunc, args, debug, lineinfo, device, fastmath, cc, opt)
266
--> 267 cres = compile_cuda(pyfunc, None, args, debug=debug, lineinfo=lineinfo,
268 nvvm_options=nvvm_options)

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/compiler_lock.py in _acquire_compile_lock(*args, **kwargs)
34 with self:
---> 35 return func(*args, **kwargs)
36 return _acquire_compile_lock

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/cuda/compiler.py in compile_cuda(pyfunc, return_type, args, debug, lineinfo, inline, fastmath, nvvm_options)
201 # Run compilation pipeline
--> 202 cres = compiler.compile_extra(typingctx=typingctx,
203 targetctx=targetctx,

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/compiler.py in compile_extra(typingctx, targetctx, func, args, return_type, flags, locals, library, pipeline_class)
692 args, return_type, flags, locals)
--> 693 return pipeline.compile_extra(func)
694

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/compiler.py in compile_extra(self, func)
428 self.state.lifted_from = None
--> 429 return self._compile_bytecode()
430

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/compiler.py in _compile_bytecode(self)
496 assert self.state.func_ir is None
--> 497 return self._compile_core()
498

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/compiler.py in _compile_core(self)
475 if is_final_pipeline:
--> 476 raise e
477 else:

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/compiler.py in _compile_core(self)
462 try:
--> 463 pm.run(self.state)
464 if self.state.cr is not None:

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/compiler_machinery.py in run(self, state)
352 patched_exception = self._patch_error(msg, e)
--> 353 raise patched_exception
354

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/compiler_machinery.py in run(self, state)
340 if isinstance(pass_inst, CompilerPass):
--> 341 self._runPass(idx, pass_inst, state)
342 else:

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/compiler_lock.py in _acquire_compile_lock(*args, **kwargs)
34 with self:
---> 35 return func(*args, **kwargs)
36 return _acquire_compile_lock

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/compiler_machinery.py in _runPass(self, index, pss, internal_state)
295 with SimpleTimer() as pass_time:
--> 296 mutated |= check(pss.run_pass, internal_state)
297 with SimpleTimer() as finalize_time:

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/compiler_machinery.py in check(func, compiler_state)
268 def check(func, compiler_state):
--> 269 mangled = func(compiler_state)
270 if mangled not in (True, False):

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/typed_passes.py in run_pass(self, state)
393 metadata=metadata)
--> 394 lower.lower()
395 if not flags.no_cpython_wrapper:

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/lowering.py in lower(self)
195 self.genlower = None
--> 196 self.lower_normal_function(self.fndesc)
197 else:

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/lowering.py in lower_normal_function(self, fndesc)
249 self.extract_function_arguments()
--> 250 entry_block_tail = self.lower_function_body()
251

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/lowering.py in lower_function_body(self)
278 self.builder.position_at_end(bb)
--> 279 self.lower_block(block)
280 self.post_lower()

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/lowering.py in lower_block(self, block)
292 loc=self.loc, errcls_=defaulterrcls):
--> 293 self.lower_inst(inst)
294 self.post_block(block)

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/lowering.py in lower_inst(self, inst)
437 ty = self.typeof(inst.target.name)
--> 438 val = self.lower_assign(ty, inst)
439 argidx = None

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/lowering.py in lower_assign(self, ty, inst)
623 elif isinstance(value, ir.Expr):
--> 624 return self.lower_expr(ty, value)
625

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/lowering.py in lower_expr(self, resty, expr)
1158 elif expr.op == 'call':
-> 1159 res = self.lower_call(resty, expr)
1160 return res

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/lowering.py in lower_call(self, resty, expr)
888 else:
--> 889 res = self._lower_call_normal(fnty, expr, signature)
890

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/lowering.py in _lower_call_normal(self, fnty, expr, signature)
1111 else:
-> 1112 argvals = self.fold_call_args(
1113 fnty, signature, expr.args, expr.vararg, expr.kws,

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/lowering.py in fold_call_args(self, fnty, signature, pos_args, vararg, kw_args)
810 "when calling %s" % (fnty,))
--> 811 argvals = [self._cast_var(var, sigty)
812 for var, sigty in zip(pos_args, signature.args)]

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/lowering.py in (.0)
810 "when calling %s" % (fnty,))
--> 811 argvals = [self._cast_var(var, sigty)
812 for var, sigty in zip(pos_args, signature.args)]

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/lowering.py in _cast_var(self, var, ty)
793 val = self.loadvar(var.name)
--> 794 return self.context.cast(self.builder, val, varty, ty)
795

/opt/conda/envs/rapids/lib/python3.9/site-packages/numba/core/base.py in cast(self, builder, val, fromty, toty)
714 except errors.NumbaNotImplementedError:
--> 715 raise errors.NumbaNotImplementedError(
716 "Cannot cast %s to %s: %s" % (fromty, toty, val))

NumbaNotImplementedError: Failed in cuda mode pipeline (step: native lowering)
Cannot cast unicode_type to Masked(string_view): %"inserted.parent" = insertvalue {i8*, i64, i32, i32, i64, i8*, i8*} %"inserted.meminfo", i8* %"arg.delim.6", 6
During: lowering "$12call_method.5 = call $8load_method.3(delim, func=$8load_method.3, args=[Var(delim, 3005899295.py:6)], kws=(), vararg=None, target=None)" at /tmp/ipykernel_2334/3005899295.py (6)

The above exception was the direct cause of the following exception:

ValueError Traceback (most recent call last)
/tmp/ipykernel_2334/3005899295.py in
6 return row["str_col"].count(delim)
7
----> 8 df.apply(delim_count, args=("b",), axis=1)

/opt/conda/envs/rapids/lib/python3.9/contextlib.py in inner(*args, **kwds)
77 def inner(*args, **kwds):
78 with self._recreate_cm():
---> 79 return func(*args, **kwds)
80 return inner
81

/opt/conda/envs/rapids/lib/python3.9/site-packages/cudf/core/dataframe.py in apply(self, func, axis, raw, result_type, args, **kwargs)
4089 raise ValueError("The `result_type` kwarg is not yet supported.")
4090
-> 4091 return self._apply(func, _get_row_kernel, *args, **kwargs)
4092
4093 def applymap(

/opt/conda/envs/rapids/lib/python3.9/contextlib.py in inner(*args, **kwds)
77 def inner(*args, **kwds):
78 with self._recreate_cm():
---> 79 return func(*args, **kwds)
80 return inner
81

/opt/conda/envs/rapids/lib/python3.9/site-packages/cudf/core/indexed_frame.py in _apply(self, func, kernel_getter, *args, **kwargs)
1820 )
1821 except Exception as e:
-> 1822 raise ValueError(
1823 "user defined function compilation failed."
1824 ) from e

ValueError: user defined function compilation failed.
```

numba version: '0.55.2'
cudf version: '22.10.00a+242.g387c5ff96d' (built from source)

cc @brandon-b-miller