SpecialUserHandle annotation: handleIncomingUser

Add some more @CanBeCURRENT and @CanBeALL annotations to various methods
in the multiuser world. In particular, handleIncomingUser is annotated,
and the concept of CURRENT_OR_SELF starts to be annotated.

Primarily, this cl covers:
* the few UserManager methods that actually can handle special users
* handleIncomingUser, and AMS methods that directly rely on it

Test: N/A Just documentation annotations
Flag: EXEMPT annotations
Bug: 373455030
Change-Id: I79cb7a99fe7eb53a43ac756b114277eb122d6b9d