[TableGen] X86 mnemonic tables backend

Add tablegen backend that generates X86 mnemonic-based opcode groupings, e.g.
`isADD`, `isTEST`, etc.

Addresses https://lists.llvm.org/pipermail/llvm-dev/2022-January/154526.html

Reviewed By: skan

Differential Revision: https://reviews.llvm.org/D121571