Reduce ActiveTransition to its token for callbacks

ActiveTransition is a somewhat-heavy object because it references all of
the TransitionInfo and SurfaceControl.Transaction data, meaning they can
not be released if another object or process is still holding onto them.

Passing out just the IBinder reduces the potential damage of a ref cycle
or slow GC from several megabytes to a few hundred bytes. We alo

Flag: EXEMPT bugfix
Test: atest WMShellUnitTests:ShellTransitionTests
Test: manually run a few transitions and use ahat to check the dumpheap
Bug: 338077587
Change-Id: Ib15c5281a284a920f3098c30f8dc401efcd475ad