[llvm] GlobalISel: Use G_UADDE when narrowing G_UMULH (PR #97194)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

"We should have a combine to form G_UADDE from this
pattern,". This will be answered in the Combiner.rst file. Are we allowed to write abstraction raising combines? In this case, I am strongly opposed. I don't want the combiner to create more legalization artefacts.

https://github.com/llvm/llvm-project/pull/97194