Skip launcher return for custom task transitions

Overriding the task exit transition requires a permission that indicates the exiting task already knows more than the launcher about what its exit is supposed to look like, so we
will let it play the animation it likes instead of the default return-to-launcher one.

Change-Id: I8f4b7292ae0863d378ec6319816e1b9cc7735c24
Test: atest transition-hotlaunch-phone
Flag: EXEMPT bugfix
Bug: 350712843