Prevent SwitchPreference widget from receiving a11y focus

Has no effect on behavior when explore by touch is turned off.

BUG: 16961152
Change-Id: I1e494d6a86f261d22d551afc43fe9e499907df6f

core/res/res/layout/preference_widget_switch.xml

@@ -21,4 +21,5 @@
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:focusable="false"
+    android:clickable="false"
     android:background="@null" />