Adding launcher permission to base whitelist

- This is a *temporary* permission that we are using to set the system
  rotation setting via the launcher settings.  The framework uses the
  same setting for forced-rotation, but this currently only is scoped to
  launcher so it makes more sense as a launcher setting than as a
  developer option (and we plan on removing it shortly).  We are working
  with jjaggi@ and caen@ to coordinate the fw and launcher settings.

Bug: 151611270
Test: Manual
Change-Id: If371cac4d580785ed1714c82a67b995a40ecf9a6

data/etc/privapp-permissions-platform.xml

@@ -62,6 +62,10 @@ applications that come with the platform
         <permission name="android.permission.MANAGE_EXTERNAL_STORAGE"/>
     </privapp-permissions>
 
+    <privapp-permissions package="com.android.launcher3">
+        <permission name="android.permission.WRITE_SECURE_SETTINGS"/>
+    </privapp-permissions>
+
     <privapp-permissions package="com.android.location.fused">
         <permission name="android.permission.INSTALL_LOCATION_PROVIDER"/>
         <permission name="android.permission.UPDATE_DEVICE_STATS"/>