The JVMTI tag hashmap has weak oop references that are handled using raw oop accesses and a G1-specific SATB enqueue call when leaking out objects from the tag map, requiring them to be marked as live by G1.

This should now be refactored to use the Access API to annotate that these are ON_PHANTOM_OOP_REF, and refactor the raw oop loads to use AS_NO_KEEPALIVE