[Partial Screen Sharing] Fix media projection cts tests on android auto

+ Makes MediaProjectionPermissionActivity use an AlertDialog instead of
  SystemUIDialog. SystemUIDialog causes problems on auto.
+ Refactors the dialogs to be dialog delegates, so that the inheritance
  from SystemUIDialog can be removed.

Flag: None
Fixes: 307193003
Test: Unit tests
Change-Id: Ie25c377c8065f6403635596caba76a7d040e4b13