[InstSimplify] look through vector select (shuffle) in min/max fold

This is an extension of the existing min/max+select fold (which already
has a very large number of variations) to allow a vector shuffle because
that's what we have in the motivating example from issue #42100.

A couple of Alive2 checks of variants (I don't know how to generalize
these in Alive):
https://alive2.llvm.org/ce/z/jUFAqT

And verify the PR42100 test:
https://alive2.llvm.org/ce/z/3EcASf

It's possible there is some generalization of the fold or a
VectorCombine/SLP answer for the motivating test, but I haven't found a
better/smaller solution yet.

We can also add even more variants here as follow-up patches. For example,
we can have shuffle followed by min/max; we also don't have this
canonicalization or the reverse:
https://alive2.llvm.org/ce/z/StHD9f

Differential Revision: https://reviews.llvm.org/D134879