Added External Display settings page

Settings page to show rotation, resolution,
enable/disable display settings for
external and overlay displays. In case
persist.demo.userrotation.package_name
sysprop is set, then the virtual
display with this will also be shown.

In case there is only one allowed display
available, then this display will be
shown right away. When there are more
than 1 displays available, then the list
of displays will be shown.

Change-Id: I186667aaba94ed6befec3a98f4a87f2b2d1f1859
Test: atest ExternalDisplayUpdaterTest
Test: atest ExternalDisplayPreferenceFragmentTest
Test: atest ResolutionPreferenceFragmentTest
Test: atest ConnectedDeviceGroupControllerTest
Bug: 340218151
Bug: 294015706
Bug: 253296253
Flag: com.android.settings.flags.rotation_connected_display_setting
Flag: com.android.settings.flags.resolution_and_enable_connected_display_setting