[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

src/com/android/settings/biometrics/face/FaceSettingsKeyguardUnlockPreferenceController.java

@@ -19,9 +19,11 @@ package com.android.settings.biometrics.face;
 import static android.provider.Settings.Secure.FACE_KEYGUARD_ENABLED;
 
 import android.content.Context;
+import android.hardware.face.FaceManager;
 import android.provider.Settings;
 
 import androidx.annotation.NonNull;
+import androidx.preference.Preference;
 
 import com.android.settings.Utils;
 import com.android.settings.biometrics.activeunlock.ActiveUnlockStatusUtils;
@@ -32,9 +34,12 @@ public class FaceSettingsKeyguardUnlockPreferenceController extends
     private static final int OFF = 0;
     private static final int DEFAULT = ON;
 
+    private FaceManager mFaceManager;
+
     public FaceSettingsKeyguardUnlockPreferenceController(
             @NonNull Context context, @NonNull String key) {
         super(context, key);
+        mFaceManager = Utils.getFaceManagerOrNull(context);
     }
 
     @Override
@@ -49,6 +54,20 @@ public class FaceSettingsKeyguardUnlockPreferenceController extends
                 FACE_KEYGUARD_ENABLED, isChecked ? ON : OFF, getUserId());
     }
 
+    @Override
+    public void updateState(Preference preference) {
+        super.updateState(preference);
+        if (!FaceSettings.isFaceHardwareDetected(mContext)) {
+            preference.setEnabled(false);
+        } else if (!mFaceManager.hasEnrolledTemplates(getUserId())) {
+            preference.setEnabled(false);
+        } else if (getRestrictingAdmin() != null) {
+            preference.setEnabled(false);
+        } else {
+            preference.setEnabled(true);
+        }
+    }
+
     @Override
     public int getAvailabilityStatus() {
         final ActiveUnlockStatusUtils activeUnlockStatusUtils =