[llvm] [TableGen][DecoderEmitter] Rework table construction/emission (PR #155889)

[Rahul Joshi via llvm-commits]

jurahul wrote:

The output you showed in https://discourse.llvm.org/t/rfc-a-new-way-to-resolve-decoding-conflicts-in-llvm-s-decoder/88104/8 looks good. It seems I have been thinking of something like a switch op as well to replace the linear search logic that we currently encode in the table. Thanks!

https://github.com/llvm/llvm-project/pull/155889