[FIRRTL] Crash when invalidating an enum

The following circuit leads to a firtool crash:

circuit c:
  module c:
    wire w: {|a: UInt<8>, b: UInt<16>|}
    w is invalid

The backtrace is the following:

all types are supported
UNREACHABLE executed at circt/lib/Dialect/FIRRTL/Transforms/SFCCompat.cpp:129!
PLEASE submit a bug report to https://github.com/llvm/circt and include the crash backtrace.
Stack dump:
0.	Program arguments: firtool test.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   0x000055a05acaa080 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 74
1  firtool   0x000055a05acaa493
2  firtool   0x000055a05aca78cb llvm::sys::RunSignalHandlers() + 146
3  firtool   0x000055a05aca9967
4  libc.so.6 0x00007b2b42e5c710
5  libc.so.6 0x00007b2b42eac83c
6  libc.so.6 0x00007b2b42e5c668 raise + 24
7  libc.so.6 0x00007b2b42e444b8 abort + 215
8  firtool   0x000055a05ac11d26
9  firtool   0x000055a05b1d847f
10 firtool   0x000055a05b1d84d7
11 firtool   0x000055a05b1d822e SFCCompatPass::runOnOperation() + 1764
12 firtool   0x000055a05c296047
13 firtool   0x000055a05c299d3a
14 firtool   0x000055a05abf0126
15 firtool   0x000055a05c29f7ad
16 firtool   0x000055a05c29646b mlir::detail::OpToOpPassAdaptor::run(mlir::Pass*, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int) + 1009
17 firtool   0x000055a05c296742 mlir::detail::OpToOpPassAdaptor::runPipeline(mlir::OpPassManager&, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int, mlir::PassInstrumentor*, mlir::PassInstrumentation::PipelineParentInfo const*) + 366
18 firtool   0x000055a05c297888
19 firtool   0x000055a05c29a7f6
20 firtool   0x000055a05c299b20
21 firtool   0x000055a05c297dfd mlir::detail::OpToOpPassAdaptor::runOnOperationAsyncImpl(bool) + 1317
22 firtool   0x000055a05c297251 mlir::detail::OpToOpPassAdaptor::runOnOperation(bool) + 59
23 firtool   0x000055a05c296022
24 firtool   0x000055a05c299d3a
25 firtool   0x000055a05abf0126
26 firtool   0x000055a05c29f7ad
27 firtool   0x000055a05c29646b mlir::detail::OpToOpPassAdaptor::run(mlir::Pass*, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int) + 1009
28 firtool   0x000055a05c296742 mlir::detail::OpToOpPassAdaptor::runPipeline(mlir::OpPassManager&, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int, mlir::PassInstrumentor*, mlir::PassInstrumentation::PipelineParentInfo const*) + 366
29 firtool   0x000055a05c297888
30 firtool   0x000055a05c29a7f6
31 firtool   0x000055a05c299b20
32 firtool   0x000055a05c297dfd mlir::detail::OpToOpPassAdaptor::runOnOperationAsyncImpl(bool) + 1317
33 firtool   0x000055a05c297251 mlir::detail::OpToOpPassAdaptor::runOnOperation(bool) + 59
34 firtool   0x000055a05c296022
35 firtool   0x000055a05c299d3a
36 firtool   0x000055a05abf0126
37 firtool   0x000055a05c29f7ad
38 firtool   0x000055a05c29646b mlir::detail::OpToOpPassAdaptor::run(mlir::Pass*, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int) + 1009
39 firtool   0x000055a05c296742 mlir::detail::OpToOpPassAdaptor::runPipeline(mlir::OpPassManager&, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int, mlir::PassInstrumentor*, mlir::PassInstrumentation::PipelineParentInfo const*) + 366
40 firtool   0x000055a05c298652 mlir::PassManager::runPasses(mlir::Operation*, mlir::AnalysisManager) + 86
41 firtool   0x000055a05c2984b1 mlir::PassManager::run(mlir::Operation*) + 1167
42 firtool   0x000055a05ab92057
43 firtool   0x000055a05ab924db
44 firtool   0x000055a05ab926c3
45 firtool   0x000055a05ab92d8f
46 firtool   0x000055a05ab931db main + 486
47 libc.so.6 0x00007b2b42e45cd0
48 libc.so.6 0x00007b2b42e45d8a __libc_start_main + 138
49 firtool   0x000055a05ab90d95 _start + 37

Reproduce the crash with the FIRRTL circuit in the issue using firtool. Start at circt/lib/Dialect/FIRRTL/Transforms/SFCCompat.cpp:129 and trace the invalid-enum invalidation path; done means this input no longer reaches the UNREACHABLE failure, with regression coverage for the case.