Updates visibility before trying to notify task stack changes

The previous activity would be immediately paused while starting
a resume-while-pausing activity, but we did not notify the
task stack changes to the listeners because the activity visibilities
weren't updated yet.

Bug: 154447447
Test: atest TaskStackChangedListenerTest

Change-Id: Id5da1c8f0fdf755341381bf49d8f48f396eebb55