[llvm] [SelectionDAG] NFC: Add target hooks to enable vector coercion in CopyToReg / CopyFromReg (PR #66134)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

We might be better off just writing an IR pass to pre-optimize these to legal integers 

https://github.com/llvm/llvm-project/pull/66134