Ask user to reboot when enabling freeform and desktop mode

The introduction of FreeformTaskListener in WM shell requires a reboot
after enabling freeform support fully. Let's add a dialog explaining the
requirement and ask user to reboot the device.

Enabling desktop mode also requires a reboot to take effect, so this CL
also adds the support to it.

There is also a cancel button to dismiss the dialog without a reboot,
just in case users need to hold off the reboot for any reason.

Bug: 215437867
Test: Pressing OK reboots the device. Pressing Cancel dismisses the
dialog.
Test: atest SettingsRoboTests:FreeformWindowsPreferenceControllerTest
Test: atest SettingsRoboTests:DesktopModePreferenceControllerTest

Change-Id: I553237a29751f73afa9fd4066241a19740872f6f

src/com/android/settings/development/RebootConfirmationDialogHost.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) 2022 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.development;
+
+/**
+ * Host of {@link RebootConfirmationDialogFragment} that provides callback when user
+ * interacts with the UI.
+ */
+public interface RebootConfirmationDialogHost {
+    /**
+     * Called when user made a decision on whether to reboot the device.
+     */
+    void onRebootConfirmed();
+}