[DAG] Fold (sra (or (shl x, c1), (shl y, c2)), c1) -> (sext_inreg (or x, (shl...

[DAG] Fold (sra (or (shl x, c1), (shl y, c2)), c1) -> (sext_inreg (or x, (shl y,c2-c1)) iff c2 >= c1

Helps with some of the AMDGPU regressions identified in D136042 where we were losing signed BFE patterns after sinking shifts behind logic ops.

Differential Revision: https://reviews.llvm.org/D136081