Add mixed transition for to-front with immersive exit

When a task is brought to front over a desktop-immersive task, the
immersive task exits (resizes back to its original bounds) in that same
transition. To animate that change using the DesktopImmersiveController
animations, the transition is moved to the mixed handler to delegate
that change and keep any other changes animated by the default handler.

Flag: com.android.window.flags.enable_fully_immersive_in_desktop
Bug: 372319492
Video: http://recall/-/MhxArsavh2DYsjdkHA7z7/Zma0YC46L9Tw1f0jEBYTz
Test: open Freefire and the Play Store in desktop, put Freefire into
immersive, then bring the store to the front from the taskbar. Verify
the Freefire exits immersive with a veiled bounds animation.

Change-Id: I348ccfbb5129344725e3ad738d9e86d03c6fbb5f