Change X86MnemonicTables to use const RecordKeeper.

This is a part of effort to have better const correctness in TableGen
backends:


https://discourse.llvm.org/t/psa-planned-changes-to-tablegen-getallderiveddefinitions-api-potential-downstream-breakages/81089

Refactor of the llvm-tblgen source into:
- a "Basic" library, which contains the bare minimum utilities to build
`llvm-min-tablegen`
- a "Common" library which contains all of the helpers for TableGen
backends. Such helpers can be shared by more than one backend, and even
unit tested (e.g. CodeExpander is, maybe we can add more over time)

Fixes #80647

Each emitter became self-contained since it has the registration of option.

Differential Revision: https://reviews.llvm.org/D144351

"TableGenBackends.h" has declarations of emitters.

1. Add comments to explain why we set `isAsmParserOnly` for XACQUIRE and XRELEASE
2. Check `X86Inst` in the constructor of `RecognizableInstrBase` so that
   we can avoid the case where one of it's field is not initialized but
   accessed by user. (e.g. in X86EVEX2VEXTablesEmitter.cpp)
3. Move `Rec` from `RecognizableInstrBase` to `RecognizableInstr` to reduce
   size of `RecognizableInstrBase`
4. Remove out-of-date comments for shouldBeEmitted() (filter() was removed)
5. Add a basic field `IsAsmParserOnly` and remove the field
   `ShouldBeEmitted` b/c we can deduce it w/ little overhead

Address comments in D122477 b/c `getMnemonic` is common to X86 and may be
used in more than one place.

Fix an issue reported by UBSan.

Test Plan:
Configure with `-DLLVM_USE_SANITIZER="Address;Undefined"`
`ninja llc`

Differential Revision: https://reviews.llvm.org/D122140

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