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:0042369de2a626f462b3d0dff8db2294aa24ffec)
Merged-In: I63e98794e1a93e3c208ee421654d73542d2bd34a
Change-Id: I63e98794e1a93e3c208ee421654d73542d2bd34a