[InstSimplify] Support vectors in simplifyWithOpReplaced()

We can handle vectors inside simplifyWithOpReplaced(), as long as
cross-lane operations are excluded. The equality can hold (or not
hold) for each vector lane independently, so we shouldn't use the
replacement value from other lanes.

I believe the only operations relevant here are shufflevector (where
all previous bugs were seen) and calls (which might use shuffle-like
intrinsics and would require more careful classification).

Differential Revision: https://reviews.llvm.org/D134348