[llvm] [SDAG] Don't treat ISD::SHL as a uniform binary operator in `ShrinkDemandedOp` (PR #92753)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon approved this pull request.

LGTM with one minor (and I prefer this to #92730)

https://github.com/llvm/llvm-project/pull/92753