[FIRRTL] Crash with out-of-bounds Index

Nobody has claimed this yet.

I noticed that the following is crashing:

```
circuit Foo:
module Foo:
input a: UInt<8>[3]
output b: UInt<8>

b <= a[UInt<99>(300)]
```

This throws an error (doesn't exit) and then crashes (`firtool Foo.fir`):

```
Foo.fir:6:12: error: out of range index '300' in vector type '!firrtl.vector, 3>'
b <= a[UInt<99>(300)]
^
LLVM ERROR: Failed to infer result type(s).
PLEASE submit a bug report to https://github.com/llvm/circt and include the crash backtrace.
Stack dump:
0. Program arguments: firtool Foo.fir
Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0 firtool 0x00000001039cf21d llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 61
1 firtool 0x00000001039cf79b PrintStackTraceSignalHandler(void*) + 27
2 firtool 0x00000001039cd566 llvm::sys::RunSignalHandlers() + 134
3 firtool 0x00000001039d14cf SignalHandler(int) + 223
4 libsystem_platform.dylib 0x00007ff80f497dfd _sigtramp + 29
5 firtool 0x00000001037856e5 std::__1::__libcpp_deallocate(void*, unsigned long, unsigned long) + 85
6 libsystem_c.dylib 0x00007ff80f3cdd24 abort + 123
7 firtool 0x000000010389f2d4 llvm::report_fatal_error(llvm::Twine const&, bool) + 388
8 firtool 0x000000010389f145 llvm::report_fatal_error(char const*, bool) + 53
9 firtool 0x000000010479c065 circt::firrtl::SubindexOp::build(mlir::OpBuilder&, mlir::OperationState&, mlir::Value, unsigned int) + 533
10 firtool 0x0000000103ed526c circt::firrtl::SubindexOp mlir::OpBuilder::create, long long>(mlir::Location, mlir::detail::TypedValue&&, long long&&) + 220
11 firtool 0x0000000103ed4fd1 circt::firrtl::SubindexOp mlir::ImplicitLocOpBuilder::create, long long>(mlir::detail::TypedValue&&, long long&&) + 81
```

Reproduce the failure with firtool Foo.fir using the FIRRTL circuit in the report. Start at circt::firrtl::SubindexOp::build, identified in the stack trace, and trace how the out-of-range diagnostic is handled; done means the invalid input reports the error without triggering the LLVM fatal crash.

Written by the indexing model from the issue text.