[AArch64][GlobalISel] Select uzp1 and uzp2

Porting the mask stuff for uzp1 and uzp2 from AArch64ISelLowering.

Add two custom opcodes: G_UZP1 and G_UZP2.

Produce them in the post-legalizer combiner when the mask checks out.

Tests:

- postlegalizer-combiner-uzp.mir verifies that we create G_UZP1 and G_UZP2.
The testcases that check that we create them come from neon-perm.ll.

- select-uzp.mir verifies that we can select G_UZP1 and G_UZP2.

Differential Revision: https://reviews.llvm.org/D81049