X86: Extend VarHandle.get() to work with instance fields.

Test: ART_HEAP_POISONING=true art/test.py --host --32 -r -t 712-varhandle-invocations
Test: ART_HEAP_POISONING=false art/test.py --host --32 -r -t 712-varhandle-invocations
Bug: 65872996
Change-Id: Ie64baf4d7d9bf3422c0e41b30d95ea903c2fabaa
2 files changed