Fix: Recent Apps not closing

Root Cause: notifyTaskStackChanged() will be invoked on activity pause
state or finishing an activity from recents.
However, launcher and recent apps are the same activity on android Q
by default, so close an app with back button(activity has been finished)
and open recent apps from launcher(activity lifecycle does not change)
will not notify listeners of task stack changes.
Solution: Notify task stack changes directly when user swipe an app away
from recent apps.

Test:
1. Close an app with back button
2. Go to recent apps and close the same app by swipe it away
3. Exit recent apps with back button
4. Open recent apps again and the app should be removed from the list.

Bug: https://issuetracker.google.com/issues/140142873

Change-Id: I1f58747d5164c45d66d53843e0b5b8c54662cdc3