[AArch64][GlobalISel] Match G_SHUFFLE_VECTOR -> insert elt + extract elt

Match a G_SHUFFLE_VECTOR with a mask that allows it to be represented as a
G_INSERT_VECTOR_ELT and a G_EXTRACT_VECTOR_ELT.

This ports `isINSMask` from AArch64ISelLowering and the portion of
`AArch64TargetLowering::LowerVECTOR_SHUFFLE` which handles the equivalent
transformation.

This provides more opportunities for matching DUP. We don't have all of the
necessary combines to actually make DUP out of these yet, but this is better for
size than the full TBL expansion for G_SHUFFLE_VECTOR.

This is a -0.1% code size improvement on CTMark/Bullet at -Os.

IR example: https://godbolt.org/z/sdcevT

Differential Revision: https://reviews.llvm.org/D97214