Reland "[AArch64] Add a tablegen pattern for UZP2."

Converts concat_vectors((trunc (lshr)), (trunc (lshr))) to UZP2
when the shift amount is half the width of the vector element.

Prioritize the ADDHN(2), SUBHN(2) patterns over UZP2.
Fixes https://github.com/llvm/llvm-project/issues/52919

Differential Revision: https://reviews.llvm.org/D130061