Custom lower and widen odd sized loads up to the alignment. The
default set of legalization actions doesn't have a way to represent
this. This fixes naturally aligned <3 x s8> and <3 x s16> loads.
This also starts moving towards eliminating the buggy and
overcomplicated legalization rules for narrowing. All the memory size
changes should be done in the lower or custom action, not NarrowScalar
/ FewerElements. These currently have redundant and ambiguous code
with the lower action.
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