Adjust Oculus Go WebXR exit arrow to the back button instead of the system button. (#3390)

Author: daoshengmu

app/src/oculusvr/res/layout/webxr_interstitial_controller.xml

@@ -89,7 +89,7 @@
                 android:layout_width="wrap_content"
                 android:layout_height="wrap_content"
                 android:layout_alignParentBottom="true"
-                android:paddingRight="40dp"
+                android:paddingRight="60dp"
                 android:layout_marginBottom="80dp"
                 android:layout_centerHorizontal="true"
                 android:scaleType="fitCenter"