Declare official platform slice

Create the notion of an official platform slice.
This includes:
- Adding a second authority to the provider
- tagging slices in xml with a platform slice flag
- Including authority in the getUri method

Bug:73359139
Test: robotests
Change-Id: I5382be138a262dbc5a8324c34aab131c5d0d5516
Merged-In: I581ee6dfcdf935f452a15e89e5d055e375ff1877

tests/robotests/src/com/android/settings/slices/SliceDataConverterTest.java

@@ -81,6 +81,7 @@ public class SliceDataConverterTest {
         assertThat(fakeSlice.getUri()).isNull();
         assertThat(fakeSlice.getFragmentClassName()).isEqualTo(fakeFragmentClassName);
         assertThat(fakeSlice.getPreferenceController()).isEqualTo(fakeControllerName);
-        assertThat(fakeSlice.getSliceType()).isEqualTo(SliceData.SliceType.SLIDER);
+        assertThat(fakeSlice.getSliceType()).isEqualTo(SliceData.SliceType.SLIDER); // from XML
+        assertThat(fakeSlice.isPlatformDefined()).isTrue(); // from XML
     }
 }