[AArch64] Use GlobalISel MatchTable Combiner Backend

Only a few minor test changes needed because I removed the "helper" suffix from the combiner name, as it's not really a helper anymore but more like the implementation itself.

Depends on D153757

NOTE: This would land iff D153757 (RFC) lands too.

Reviewed By: aemerson

Differential Revision: https://reviews.llvm.org/D153850