[LV] Support Interleaved Store Group With Gaps

Teach LV to use masked-store to support interleave-store-group with
gaps (instead of scatters/scalarization).

The symmetric case of using masked-load to support
interleaved-load-group with gaps was introduced a while ago, by
https://reviews.llvm.org/D53668; This patch completes the store-scenario
leftover from D53668, and solves PR50566.

Reviewed by: Ayal Zaks

Differential Revision: https://reviews.llvm.org/D104750