Update App blocking UX behavior.

Previously, when an unsafe (non distraction optimized) app is blocked,
the unsafe task is killed and the Home activity is put in the task
stack behind the new App blocking activity.  So, when the app blocking
activity is automatially dismissed by a timer, we will go back to the Home
activity.

Now, the App blocking activity cannot be dismissed except by explicity
clicking something on the SysUI navigation bar.

This change does the foll:
1. Removes putting the Home activity in the task stack as the App
blocking activity is not dismissed automatically.
2. Doesn't kill the currently blocked activity, since if went back to a
safer state (eg parked), the blocked activity can resume.
3. The app blocking activity should dismiss itself when the UX
restrictions are lifted by listening to the UX restrictions.  So, when
the App blocking activity is dismissed, we will get back to the
previously blocked activity that is still in the stack (as per point 2
above).

Bug: 77518475
Test: Tested that the blocked activity can resume when going from drive
to park.  Also tested the same behavior for launching a new app, since
launcher still tries to launch the app regardless of the current UX
restrictions.

Change-Id: Ie561a8d8790c0871690e89083fd8483b03b1133b
2 files changed