Stop all activities behind presentation

There's a security concern with Presentation API and Connected
Displays (CD), where malicious apps can show a presentation on other
apps and do "tap jacking". This is a new scenario with CD because
apps can now be launched on external displays in extended/projected
mode.

To prevent this problem, we've agreed that we should stop all the
activities below a presentation on the same display. This way,
even if a transparent presentation is created, other apps become
completely hidden, and the user won't inject input events intended
for other apps.

Flag: com.android.window.flags.enable_presentation_for_connected_displays
Bug: 393454633
Test: WindowManagerServiceTests#testPresentationHidesActivitiesBehind
Change-Id: I26108aa0bc0cac320c8fb50ea67543981ab77e23