[ScalarizeMaskedMemIntrin] Use pointer alignment from pointer of...

[ScalarizeMaskedMemIntrin] Use pointer alignment from pointer of masked.compressstore/expandload. (#83519)

Previously we used Align(1) for all scalarized load/stores from
masked.compressstore/expandload.
For targets not supporting unaligned accesses, it make backend need to
split
aligned large width loads/stores to byte loads/stores.
To solve this performance issue, this patch preserves the alignment of
base
pointer after scalarizing.