ve.ce.Surface: Prevent focus loss on the document node in Opera

Opera triggers 'blur' on the document node when clicking on any <a>
link and never trigger 'focus' until after the user blurs the document
node *again* (by clicking outside of it or pressing 'Esc').

This causes the change polling to stop (SurfaceObserver#stop is called
without a subsequent call to SurfaceObserver#start).

To avoid this let's bind a delegated 'focus' event on all <a> links
inside the document and refocus it whenever that happens.

Bug: 47793
Change-Id: I7962f59bd02e075f91e42e6514b390c0d0feb3ab
Merge "ve.ce.Surface: Prevent focus loss on the document node in Opera"