[llvm] [AArch64][GlobalISel] Add push_mul_through_s/zext (PR #141551)

[David Green via llvm-commits]

davemgreen wrote:

Some of the neon-dotreduce.ll cases are worse, we are pretty bad at dealing with odd sized extends at the moment and this turns it from 1 bad extend into 2 bad extends. It should be fixed separately when they get through legalization more efficiently.

https://github.com/llvm/llvm-project/pull/141551