Unexport ControlsActivity

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

Bug: 404256832
Flag: EXEMPT bugfix
Test: atest ControlsSettingsDialogManagerImplTest
(cherry picked from commit 0042369de2a626f462b3d0dff8db2294aa24ffec)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:2903f50717163c4368ef3379be53c55f9e9e3966)
Merged-In: I63e98794e1a93e3c208ee421654d73542d2bd34a
Change-Id: I63e98794e1a93e3c208ee421654d73542d2bd34a