Unexport ControlsActivity

Also do not draw non-system windows on top of ControlsSettingsDialog

Fix: 404256832
Flag: EXEMPT bugfix
Test: atest ControlsSettingsDialogManagerImplTest
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:79c8c73949f51359dca40ba1b9286c866d9844cf)
Merged-In: I6280b501b799596099935dc61ecef0b431dd8333
Change-Id: I6280b501b799596099935dc61ecef0b431dd8333