ART-tests: Remove DX dependency from 646-checker-hadd(-alt)?-(short|char)

These tests had two issues with D8: (1) And operands swapped and (2) due
to unfortunate register-allocation the live ranges of certain registers
escaped into environment. This CL updates the CHECKS to match the D8-
generated code and refactors a few expressions which results in
shorter live ranges.

Test: art/test.py -r -b --host -t 646-checker-hadd-alt-char
Test: art/test.py -r -b --host -t 646-checker-hadd-alt-short
Test: art/test.py -r -b --host -t 646-checker-hadd-char
Test: art/test.py -r -b --host -t 646-checker-hadd-short
Bug: 65168732
Change-Id: Iaa41853123f57ac4d996527414b2f434faa7c4f0