Enable remote transition animations to append to the finish transaction

Adds a parameter to the IRemoteTransitionFinishedCallback. This
transaction will be merged into the finish transaction before it is
applied. This is needed by transitions like live-tile recents where
the end-state of the transition is altered during the "animation".

Bug: 172695387
Test: open app, swipe up to overview, resume that same app, screen
      shouldn't turn black anymore.
Change-Id: I6fa1e22288ce087ad17fdfc950a8419e6ba61a47