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/TouchGesturesButtonPreferenceController.java

@@ -21,6 +21,7 @@ import static com.android.systemui.shared.Flags.newTouchpadGesturesTutorial;
 import android.app.settings.SettingsEnums;
 import android.content.Context;
 import android.content.Intent;
+import android.hardware.input.InputSettings;
 import android.os.UserHandle;
 import android.util.FeatureFlagUtils;
 
@@ -75,7 +76,14 @@ public class TouchGesturesButtonPreferenceController extends BasePreferenceContr
     @Override
     public int getAvailabilityStatus() {
         boolean isTouchpad = InputPeripheralsSettingsUtils.isTouchpad();
-        return isTouchpad ? AVAILABLE : CONDITIONALLY_UNAVAILABLE;
+        if (isTouchpad) {
+            // If the user's disabled touchpad system gestures in the accessibility settings, the
+            // tutorial won't work or be relevant, so disable the button.
+            return InputSettings.useTouchpadSystemGestures(mContext) ? AVAILABLE
+                    : DISABLED_DEPENDENT_SETTING;
+        } else {
+            return CONDITIONALLY_UNAVAILABLE;
+        }
     }
 
     private void showTouchpadGestureEducation() {