x86/string compression: Use TESTB instead of TESTL in String.charAt().

And fix disassembly of the now unused TESTL.

Test: testrunner.py --host with string compression enabled.
Test: Manual inspection of dump-oat output.
Bug: 35433135
Bug: 31040547
Change-Id: I36c955bc1f2243954ecc315266a2f3fce5d87693
3 files changed