[LV] Recognize intrinsic min/max reductions

This extends the reduction logic in the vectorizer to handle intrinsic
versions of min and max, both the floating point variants already
created by instcombine under fastmath and the integer variants from
D98152.

As a bonus this allows us to match a chain of min or max operations into
a single reduction, similar to how add/mul/etc work.

Differential Revision: https://reviews.llvm.org/D109645