[AArch64] Identify SAD pattern

(ABS (SUB (EXTEND a), (EXTEND b))) to ZERO_EXTEND((UABD a, b))
(ABS (SUB (SIGN_EXTEND a), (SIGN_EXTEND b))) to ZERO_EXTEND((SABD a, b))

This partially solves the bug: https://bugs.llvm.org/show_bug.cgi?id=46888
Meta ticket: https://bugs.llvm.org/show_bug.cgi?id=46929

Differential Revision: https://reviews.llvm.org/D88742