Add a11y setting for disabling touchpad system gestures

Screenshots:
* The new setting: http://shortn/_9JL6nMS3cR
* The disabled "Learn touchpad gestures" button and accompanying footer
  when the setting is off: http://shortn/_FTcNTQAGYj

Test: disable the setting, check three- and four-finger swipes on the
      touchpad stop working; re-enable, check they work again
Test: check the toggle and heading both hide correctly when flag is off
      or no touchpad is connected
Test: check the "Learn touchpad gestures" button is disabled with an
      explanation when gestures are disabled
Bug: 353947750
Bug: 374965372
Flag: com.android.hardware.input.touchpad_system_gesture_disable
Change-Id: Ie7a6ea4e9ddd34710d07f78ab96598207aac4228

src/com/android/settings/inputmethod/TrackpadGesturesDisabledFooterPreferenceController.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2024 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.inputmethod;
+
+import android.content.Context;
+import android.hardware.input.InputSettings;
+
+import com.android.settings.core.BasePreferenceController;
+
+public class TrackpadGesturesDisabledFooterPreferenceController extends BasePreferenceController {
+
+    public TrackpadGesturesDisabledFooterPreferenceController(Context context, String key) {
+        super(context, key);
+    }
+
+    @Override
+    public int getAvailabilityStatus() {
+        return InputSettings.useTouchpadSystemGestures(mContext) ? CONDITIONALLY_UNAVAILABLE
+                : AVAILABLE;
+    }
+}