Enable jquery.ui.position on mobile

Enable jquery.ui.position on mobile

Although this module is deprecated it appears to be used in isolation
from jquery.ui in key extensions such as Translate. To aid extensions
who need to transition away from it we should make this available on mobile.

This module does not appear to be loaded on startup and is the only
non-mobile targetted module used by the Translate extension so enabling
this will give us benefit.

This also fits in with the long term plan
of deprecating the targets field altogether.

Change-Id: Ib381b820c69832f9aa6fce01f5dae8b4f50d66fa