Support following typing focus in window mode [3/n].

There are 3 milestones in this feature.
1. Refactor the callbacks for Accessibility in WindowManagerInternal.
2. Implement this feature in such new architecture.
3. Implement the setting choice in preference page.

This CL is for the 3rd milestone.

We add a preference key "magnification_follow_typing" to access and
update the ACCESSIBILITY_MAGNIFICATION_FOLLOW_TYPING_ENABLED value
which controls its corresponding preference page UI.

Bug: 194668976
Test: make RunSettingsRoboTests ROBOTEST_FILTER=
	MagnificationFollowTypingPreferenceControllerTest
	ToggleScreenMagnificationPreferenceFragmentTest
Change-Id: Ib2602c997a535c1acca6a7ddd7bb2c25921f9280

src/com/android/settings/accessibility/MagnificationFollowTypingPreferenceController.java

@@ -0,0 +1,80 @@
+/*
+ * 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.accessibility;
+
+import static com.android.settings.accessibility.AccessibilityUtil.State.OFF;
+import static com.android.settings.accessibility.AccessibilityUtil.State.ON;
+
+import android.content.Context;
+import android.provider.Settings;
+
+import androidx.lifecycle.Lifecycle;
+import androidx.lifecycle.LifecycleObserver;
+import androidx.lifecycle.OnLifecycleEvent;
+import androidx.preference.PreferenceScreen;
+import androidx.preference.SwitchPreference;
+
+import com.android.settings.R;
+import com.android.settings.core.TogglePreferenceController;
+
+/** Controller that accesses and switches the preference status of following typing feature */
+public class MagnificationFollowTypingPreferenceController extends TogglePreferenceController
+        implements LifecycleObserver {
+
+    static final String PREF_KEY = "magnification_follow_typing";
+
+    private SwitchPreference mFollowTypingPreference;
+
+    public MagnificationFollowTypingPreferenceController(Context context, String preferenceKey) {
+        super(context, preferenceKey);
+    }
+
+    @Override
+    public int getAvailabilityStatus() {
+        return AVAILABLE;
+    }
+
+    @Override
+    public boolean isChecked() {
+        return Settings.Secure.getInt(mContext.getContentResolver(),
+                Settings.Secure.ACCESSIBILITY_MAGNIFICATION_FOLLOW_TYPING_ENABLED, ON) == ON;
+    }
+
+    @Override
+    public boolean setChecked(boolean isChecked) {
+        return Settings.Secure.putInt(mContext.getContentResolver(),
+                Settings.Secure.ACCESSIBILITY_MAGNIFICATION_FOLLOW_TYPING_ENABLED,
+                (isChecked ? ON : OFF));
+    }
+
+    @Override
+    public int getSliceHighlightMenuRes() {
+        return R.string.menu_key_accessibility;
+    }
+
+    @Override
+    public void displayPreference(PreferenceScreen screen) {
+        super.displayPreference(screen);
+        mFollowTypingPreference = screen.findPreference(getPreferenceKey());
+    }
+
+    // TODO(b/186731461): Remove it when this controller is used in DashBoardFragment only.
+    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
+    void onResume() {
+        updateState(mFollowTypingPreference);
+    }
+}