Add PrefController in XML support

Add the ability to define a Preference Controller
in xml using the 'controller' tag.

This is useful for two reasons:
- It allows the controllers to be instantiated via
reflection for Slices and Dashboard fragment
- Removes the requirement that controllers be defined manually
in Fragments

In order to be instantiable, they must have a unified construction
following either:

  ClassName(Context)
  ClassName(Context, String)

Also added a robotest that verifies that all controllers defined
in XML follow the constructor schema, and extend
BasePreferenceController.

Test: robotests
Bug: 67996923
Change-Id: I304b35dc666daebecf0c9e286696f3f2a510704a

tests/robotests/src/com/android/settings/deviceinfo/SystemUpdatePreferenceControllerTest.java

@@ -57,7 +57,9 @@ public class SystemUpdatePreferenceControllerTest {
     @Before
     public void setUp() {
         MockitoAnnotations.initMocks(this);
-        mController = new SystemUpdatePreferenceController(mContext, mUserManager);
+
+        when(mContext.getSystemService(Context.USER_SERVICE)).thenReturn(mUserManager);
+        mController = new SystemUpdatePreferenceController(mContext);
         mPreference = new Preference(RuntimeEnvironment.application);
         mPreference.setKey(mController.getPreferenceKey());
         when(mScreen.findPreference(mController.getPreferenceKey())).thenReturn(mPreference);
@@ -82,7 +84,7 @@ public class SystemUpdatePreferenceControllerTest {
 
         mController.updateNonIndexableKeys(keys);
 
-        assertThat(keys.size()).isEqualTo(1);
+        assertThat(keys).hasSize(1);
     }
 
     @Test
@@ -94,8 +96,8 @@ public class SystemUpdatePreferenceControllerTest {
 
     @Test
     public void updateState_shouldSetToAndroidVersion() {
-        mController = new SystemUpdatePreferenceController(
-                RuntimeEnvironment.application, mUserManager);
+        mController = new SystemUpdatePreferenceController(RuntimeEnvironment.application);
+
         mController.updateState(mPreference);
 
         assertThat(mPreference.getSummary())