[llvm] [AArch64][SVE] Fold nested boolean UMIN trees (PR #209234)

[Matthew Devereau via llvm-commits]

MDevereau wrote:

I've updated this with the assumption that constant operands are canonicalised to be on the RHS from #211249 when converting cmpne/cmpeq to UMin instructions. The previous version of this patch which combined via cmpne can be easier done through nested UMins.

https://github.com/llvm/llvm-project/pull/209234