[llvm] [X86][MC] Support encoding/decoding for APX variant MUL/IMUL/DIV/IDIV instructions (PR #76919)

[Phoebe Wang via llvm-commits]

https://github.com/phoebewang approved this pull request.

LGTM expect for some typos.

https://github.com/llvm/llvm-project/pull/76919