[llvm] [AArch64][LoopIdiom] Generalize AArch64LoopIdiomTransform into LoopIdiomTransform (PR #94081)

[Philip Reames via llvm-commits]

preames wrote:

Can we please split this into two changes, one which does the move and rename, and a second which adds the new functionality?  This diff is slightly confusing as a reader.

Naming wise, maybe LoopIdiomVectorizer?  And update the comment to be really explicit about the goal being to eventually kill this off as the vectorizer grows more powerful?

https://github.com/llvm/llvm-project/pull/94081