[llvm] [TableGen][DecoderEmitter] Add extractBits() overloads (PR #159405)

[Sergei Barannikov via llvm-commits]

s-barannikov wrote:

I'll have to drop `static_asserts` because they trigger on code that will never be executed (remember that decodeToMCInst has switch cases for all instruction widths). It would be nice if we enabled `--specialize-decoders-per-bitwidth` unconditionally, then the asserts could be helpful.


https://github.com/llvm/llvm-project/pull/159405