[llvm] [InstCombine] Sink widening casts used only by extractelements (PR #201529)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

Our policy on InstCombine folds that affect vector types has gotten stricter since the original fold was added to InstCombine. I'm not saying all existing fold need to be looked at again, but this seems a good candidate, especially as VectorCombine has a relatively simple cost driven approach for multi-use folds.

https://github.com/llvm/llvm-project/pull/201529