Separate PiP animation from unrelated intent-provided remoteAnimations

Some launch methods (eg. starting activity from notification) include
remoteanimations in the intent but don't know how to handle PiP entry
(which requires 2 transitions currently). To remedy this, use the
mixed-handler to check for this potential situation and then split
the transition among the remoteanimation and the pip-handler.

Bug: 267897440
Test: Open a pip-able app, launch another activity from notification
Change-Id: I2253fb0c34602370124fcaefc33a8360cdc8fea9