Pass in finishTransaction to TransitionHandler#startAnimation

When iterating through registered transitions and finding one and
marking as active, WM sets a reset transition which runs at when the
transition handler runs its finish callback. However, not all transition
handler wants a complete reset of the transition; in PiP's case, it
actually wants to set the final position to the new PiP x and y
coordinates. Passing in the finish transition to #startAnimation will allow
each transition handler to customize and overwrite values as necessary.

Bug: 165793917
Test: Enable Transitions, enter PIP - PIP animates correctly now
Change-Id: I741a04c1a9123c924383168c0db48646ef34059d