[Biometric Onboarding & Edu] Update face settings page

- Added a feature provider for face settings page in FaceFeatureProvider
  for customization
- When face is deleted, disabled the settings buttons instead of hiding
  them.
- Updated new UX style for add/remove face button.

Bug: 370940762
Test: atest FaceSettingsEnrollButtonPreferenceControllerTest
            FaceSettingsFooterPreferenceControllerTest
Test: manual - 1. Enroll face
               2. Go Face Settings page and remove face
	       3. Enroll face again
Flag: com.android.settings.flags.biometrics_onboarding_education

Change-Id: I490e647523eeff2dd1a58aab07f638e3e5e0ffb8

tests/unit/src/com/android/settings/biometrics/face/FaceSettingsEnrollButtonPreferenceControllerTest.java

@@ -24,6 +24,7 @@ import static org.mockito.Mockito.verify;
 import android.content.Context;
 import android.widget.Button;
 
+import androidx.preference.Preference;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 
 import org.junit.Before;
@@ -43,6 +44,8 @@ public class FaceSettingsEnrollButtonPreferenceControllerTest {
     @Mock
     private Button mButton;
     @Mock
+    private Preference mPreference;
+    @Mock
     private FaceSettingsEnrollButtonPreferenceController.Listener mListener;
 
     private FaceSettingsEnrollButtonPreferenceController mController;
@@ -65,4 +68,12 @@ public class FaceSettingsEnrollButtonPreferenceControllerTest {
         assertThat(mController.isClicked()).isTrue();
         verify(mListener).onStartEnrolling(any());
     }
+
+    @Test
+    public void testOnPreferenceClick() {
+        mController.onPreferenceClick(mPreference);
+
+        assertThat(mController.isClicked()).isTrue();
+        verify(mListener).onStartEnrolling(any());
+    }
 }