[llvm] [VectorCombine] Add support for zext/sext/trunc to shuffleToIdentity (PR #92696)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> I did a partial review of the existing code, and my suggestions are along the lines of the following diff. I think it would be nice if you could improve the existing code as an NFC patch before landing this patch.

I additionally think the long lambdas make it hard to reason about the code. Might be good to split them out into static functions.

https://github.com/llvm/llvm-project/pull/92696