Provide one click highlighting of entire URI in the address box

[FGrose]

When one clicks in the address box, it would be more usable if the entire address would be highlighted.

This makes copying the address or pasting over the current address much easier.

A second click would release the highlight, if one wanted to edit a portion of the URI.

These features would match the more common use cases.

An alternative would be to provide a click target at the left or right ends (or both) of the the address box (in the semi-circles) that would highlight the entire address. That way, one would click there if the entire URI was the goal, or within the address if an edit were the goal.

[manuq]

This is being worked on #3499 . Closing.