[mlir][Linalg] Add support for min/max reduction vectorization in linalg.generic

This patch extends Linalg core vectorization with support for min/max reductions
in linalg.generic ops. It enables the reduction detection for min/max combiner ops.
It also renames MIN/MAX combining kinds to MINS/MAXS to make the sign explicit for
floating point and signed integer types. MINU/MAXU should be introduce din the future
for unsigned integer types.

Reviewed By: pifon2a, ThomasRaoux

Differential Revision: https://reviews.llvm.org/D110854