Add credential management app preference to Settings

Background
* This is part of the work to support
  a credential management app on
  unmanaged devices.
Changes
* Add a preference controller which will only
  be enabled if there is a credential management app.
* Add a fragment to display details on the credential
  management app and its policy. Add a remove button
  to remove the credential management app.
* Link CredentialManagementAppAdapter to new fragment
  and add expander.

Manual Testing
* Verify preference is disabled if there is no credential
  management app.
* Verify preference summary shows credential mangement
  app name if a credential management app exists.
* Verify fragment details page displays the
  authentication policy correctly.

Bug: 165641221
Test: Manual testing
      make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.security.CredentialManagementAppFragmentTest
      make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.security.CredentialManagementAppControllerTest
Change-Id: I06d6b88d0c89022f7a6cbf3031834defcb54bd51

src/com/android/settings/security/CredentialManagementAppPolicyController.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.security;
+
+import static com.android.settings.core.BasePreferenceController.AVAILABLE_UNSEARCHABLE;
+
+import android.content.Context;
+
+import androidx.preference.PreferenceGroup;
+import androidx.preference.PreferenceScreen;
+
+import com.android.settings.core.BasePreferenceController;
+
+/**
+ * Controller that shows the credential management app's authentication policy.
+ */
+public class CredentialManagementAppPolicyController extends BasePreferenceController {
+
+    public CredentialManagementAppPolicyController(Context context, String preferenceKey) {
+        super(context, preferenceKey);
+    }
+
+    @Override
+    public int getAvailabilityStatus() {
+        return AVAILABLE_UNSEARCHABLE;
+    }
+
+    @Override
+    public void displayPreference(PreferenceScreen screen) {
+        super.displayPreference(screen);
+
+        PreferenceGroup group = screen.findPreference(getPreferenceKey());
+        group.addPreference(new CredentialManagementAppPolicyPreference(group.getContext()));
+    }
+}