[llvm] [GlobalISel]: G_UNMERGE_VALUES for vectors with different element sizes (PR #133335)

[Robert Imschweiler via llvm-commits]

ro-i wrote:

Yes, that's what the current version of this PR tries to do. That's why I added the check in `tryCombineMergeLike`, which prevents this unmerge from being built. I guess that there are multiple other possible places, so I'd be happy to implement this somewhere else if you think it would make more sense there!

https://github.com/llvm/llvm-project/pull/133335