[llvm-branch-commits] [WebAssembly] Port WebAssemblyPostLegalizerCombiner (PR #218101)

[Aiden Grossman via llvm-branch-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/218101

Standard NewPM pass porting. Again, we do need to move the rule parsing
into the per-MF implementation since it's hard to get the type
definition into the NewPM pass definition, but this should be low
overhead.