Move 712-varhandle-invocations to API level 28

Bug: 65168732
Test: art/test/run-test  --no-relocate --64 --build-with-javac-dx --runtime-option -Xcheck:jni --never-clean --host 712-varhandle-invocations
Change-Id: Ie8cab287541dd82324cc8bb8365bd31c552d0518
2 files changed