Make some gesture related slices public.

Only PreferenceControllers with isPublicSlice() set to true are exposed
to other apps. Others will be Settings only.

Bug: 141088937
Test: robotests
Change-Id: I0b54e752c5982f13193590db47dc3a84dde5311d

src/com/android/settings/gestures/DoubleTapScreenPreferenceController.java

@@ -77,6 +77,11 @@ public class DoubleTapScreenPreferenceController extends GesturePreferenceContro
         return TextUtils.equals(getPreferenceKey(), "gesture_double_tap_screen");
     }
 
+    @Override
+    public boolean isPublicSlice() {
+        return true;
+    }
+
     @Override
     public boolean setChecked(boolean isChecked) {
         return Settings.Secure.putInt(mContext.getContentResolver(), SECURE_KEY,