Fix the problem that the unknown item will be announced when

using Switch Access.

- Disable the importantForAccessibility of the
  SettingsMainSwitchBar's parent layout.

Fix: 182227784
Test: robotest and operate the switch preference manually
Change-Id: I5e0e4bb972f6996192d5a30525bb5370a006b115

res/layout/preference_widget_main_switch.xml

@@ -15,10 +15,11 @@
   limitations under the License.
   -->
 
-<LinearLayout
+<FrameLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
-    android:layout_height="wrap_content">
+    android:layout_height="wrap_content"
+    android:importantForAccessibility="no">
 
     <com.android.settings.widget.SettingsMainSwitchBar
         android:id="@+id/main_switch_bar"
@@ -26,4 +27,4 @@
         android:layout_height="wrap_content"
         android:layout_width="match_parent" />
 
-</LinearLayout>
+</FrameLayout>