[mlir][vector] Masking support for reductions in Linalg vectorizer

[mlir][vector] Masking support for reductions in Linalg vectorizer

This patch enables vectorization of reductions in Linalg vectorizer
using the vector.mask operation. It also introduces the logic to slice
and propagate the vector mask of a masked multi-reduction to their
respective lowering operations.

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D141571