PrivacyDotWindowController: prevent crash when removing views from WM

When a display is removed right after being added, there was a crash
in PrivacyDotWindowController when trying to remove the views from
WindowManager.

To prevent this crash, we are now doing two things:
1. Ensure the stop/removal code runs on the same ui thread as the code
   that starts/adds views to WM.
2. Wrap the removal with try/catch for the worst case scenario.

Test: PrivacyDotWindowControllerTest
Fixes: 424739989
Flag: com.android.systemui.shared.status_bar_connected_displays
Change-Id: I06bc7dab742bda35125c9769a0ab6662eb02de86