JVMTI Force early return

Add support for can_force_early_return jvmti capability. This allows
one to force java frames to exit early. Exited frames have all of
their normal locks released.

We implement this by modifying the existing method exit events to
allow one to modify the exit value during the callback. This is used
to implement ForceEarlyReturn by adding internal-only events that will
change the return value of methods once they return (using
kForcePopFrame) avoiding the need to modify the actual interpreter
very deeply. This also makes it simple to continue to use the standard
deoptimization functions to force the actual return.

In order to simplify book-keeping the internal event is refcounted,
not associated with any specific jvmtiEnv, and only settable on
specific threads. The internal event is added by the ForceEarlyReturn
function and then removed by the MethodExit event when we update the
return value.

Bug: 130028055
Test: ./test.py --host
Change-Id: Ifa44605b4e8032605f503a654ddf4bd2fc6b60bf

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