Prevent onHandleDestroyed from being called w/ mStateLock

Now that we can apply transactions from the main thread, we can possibly
call onHandleDestroyed while mStatelock is held.  Add a copy outside the
lock boundaries to prevent this

Bug: 131421215
Test: build, boot, libsurfaceflinger_unittest
Change-Id: I0c7a3852d6706ec9df5467e5f4bd23061f11fa11