Fix connected display dialog overlap with 3 buttons nav

The content insets are now aware of the navbar size.
Note that this can't be put in the base class (SystemUIBottomSheet), as
it is specific to the content of the dialog. The base class only cares
about the window.

Fixes: 306541121
Test: SystemUIBottomSheetDialogTest + manually trying all navigation
       modes and orientations
Change-Id: I3fc5e152026b93c6415a3f5bd0d011c3c86e0fd8