[Media Projection] Fix permission dialog buttons being clipped

When setting the display size to something large, the buttons can be
clipped in some locales, as there is not enough space to fit them
horizontally.

The fix is to use ButtonBarLayout, which automatically switches to
vertical orientation when there is not enough horizontal space.

Test: Manual
Fixes: 322847977
Flag: NONE
Change-Id: I3076a9c10709128fd393ed0cd1f8589d8f694b65