[PB] Adjust default cross animation for floating window.

- When playing cross-activity animation in a floating task, crop the
background surface so it won't occludes wallpaper.
- Do not play default cross-task/back-to-home animation for the
floating task for now.

Flag: EXEMPT Bugfix
Bug: 358643645
Test: move task into desktop mode, trigger cross-activity animation and
verify background layer won't occludes wallpaper. Also verify no default
cross-task animation when closing a task.

Change-Id: I5dd3a3ccf509e6ea299925e74c852bf1be6706e1