[IA] Support vp.store in lowerinterleavedStore (#149605)

Follow up to 28417e64, and the whole line of work started with 4b81dc7.

This change merges the handling for VPStore - currently in
lowerInterleavedVPStore - into the existing dedicated routine used in
the shuffle lowering path. This removes the last use of the dedicated
lowerInterleavedVPStore and thus we can remove it.

This contains two changes which are functional.

First, like in 28417e64, merging support for vp.store exposes the
strided store optimization for code using vp.store.

Second, it seems the strided store case had a significant missed
optimization. We were performing the strided store at the full unit
strided store type width (i.e. LMUL) rather than reducing it to match
the input width. This became obvious when I tried to use the mask
created by the helper routine as it caused a type incompatibility.

Normally, I'd try not to include an optimization in an API rework, but
structuring the code to both be correct for vp.store and not optimize
the existing case turned out be more involved than seemed worthwhile. I
could pull this part out as a pre-change, but its a bit awkward on it's
own as it turns out to be somewhat of a half step on the possible
optimization; the full optimization is complex with the old code
structure.

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Co-authored-by: Craig Topper <craig.topper@sifive.com>

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