Duplicate variables in function

Input:
```
package riscv;
function string func();
automatic string str = "str";
return "";
endfunction
endpackage
```
Output:
```
\_package: riscv (riscv::), id:23 test.sv:1:1: , endln:6:11, parent:unnamed, parID:22
|vpiName:riscv
|vpiFullName:riscv::
|vpiDefName:riscv
|vpiTaskFunc:
\_function: (riscv::func), id:24, line:2:3, endln:5:14, parent:riscv::, parID:23
|vpiName:func
|vpiFullName:riscv::func
|vpiVariables:
\_string_var: (riscv::func::str), id:25, line:3:22, endln:3:25, parent:riscv::func, parID:24
|vpiName:str
|vpiFullName:riscv::func::str
|vpiAutomatic:1
|vpiVisibility:1
|vpiReturn:
\_string_var: , id:14, line:2:12, endln:2:18
|vpiStmt:
\_begin: (riscv::func), id:26, parent:riscv::func, parID:24
|vpiFullName:riscv::func
|vpiVariables:
\_string_var: (riscv::func::str), id:27, line:3:22, endln:3:25, parent:riscv::func, parID:26
|vpiName:str
|vpiFullName:riscv::func::str
|vpiAutomatic:1
|vpiStmt:
\_assign_stmt: , id:28, line:3:22, endln:3:33, parent:riscv::func, parID:26
|vpiRhs:
\_constant: , id:19, line:3:28, endln:3:33, parID:18
|vpiDecompile:str
|vpiSize:3
|STRING:str
|vpiConstType:6
|vpiLhs:
\_string_var: (riscv::func::str), id:29, line:3:22, endln:3:25, parID:28
|vpiName:str
|vpiFullName:riscv::func::str
|vpiAutomatic:1
|vpiStmt:
\_return_stmt: , id:30, line:4:5, endln:4:11, parent:riscv::func, parID:26
|vpiCondition:
\_constant: , id:21, line:4:12, endln:4:14, parID:20
|STRING:
|vpiConstType:6
|vpiInstance:
\_package: riscv (riscv::), id:23 test.sv:1:1: , endln:6:11, parent:unnamed, parID:22
```

Note the three instances of `string_var` variable `str` with ids 25, 27 and 29. Issue is not specific to `string` only.

Start by reproducing the supplied SystemVerilog package and inspecting the generated VPI/UHDM output for the function variable. Trace why str appears as three string_var instances, then verify the output no longer duplicates the variable and that the same behavior is corrected for types beyond string.

Written by the indexing model from the issue text.