[4/n] Add enter and exit desk reason from controller

Add enterReason and exitReason for all method calls to
addDeskActivationChanges and addDeskDeactivationChanges and keep reasons
in DeskTransition to be logged when DesksTransitionObserver is ready to
handle desk transition.

Flag: EXEMPT logging
Bug: 423560267
Test: atest DesktopTasksControllerTest
Change-Id: I230d466896d523e00af9037b11a30a50dce6d9a5