[llvm] [RFC][MC] Cache MCRegAliasIterator (PR #93510)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

The real fix should be to switch all uses of MCRegAliasIterator to use MCRegUnitIterator instead. No liveness infrastructure should operate in terms of aliases 

https://github.com/llvm/llvm-project/pull/93510