[llvm] add narrowExtractedVectorUnaryOp to simplify cast nodes (PR #87977)

[Vedant Paranjape via llvm-commits]

vedantparanjape-amd wrote:

> Yes, you're right - we're getting stopped by legality tests as we have poor src/dst legality tests for cast ops.

I see, is it something that can be worked on ?

https://github.com/llvm/llvm-project/pull/87977