[DAG][AArch64][ARM] Combine abd(sub(x, y)) to abd if the sub is nsw

This implements the fold (abs (sub nsw x, y)) -> abds(x, y). Providing
the sub is nsw this appears to be valid without the extensions that are
usually used for abds. https://alive2.llvm.org/ce/z/XHVaB3. The
equivalent abdu combine seems to not be valid.

Differential Revision: https://reviews.llvm.org/D141665