Make sure both transition start/end callback sent

Fixed the case that swipe-pip-to-home animator is created in Launcher
but there is actually no PiP transition followed.

When Launcher detects an app can auto enter PiP,
PipTaskOrganizer#startSwipePipToHome will get called and send out the
transition started callback, in certain cases, like what's described in
the bug, there is no PiP transition followed by that and therefore,
there will be no transition finished callback.

With the previously merged change ag/28059459, this in turn leaves
Launcher gesture in disabled state.

Addressed this by moving sendOnPipTransitionStarted to
PipTransition#handleSwipePipToHomeTransition, where we also call
sendOnPipTransitionFinished to make sure these two calls are always sent
in the auto-enter-pip case (with shell transition being enabled).

Flag: EXEMPT bugfix
Video: http://recall/-/aaaaaabFQoRHlzixHdtY/cFTnHKLEK3XVGCeiR2vY3w
Bug: 350989174
Bug: 340724371
Test: Swipe YouTube to home with Circle-to-Search being present
Change-Id: I1bdf4964ddf45eefb792b3ff42c4f707b428a984