This changes the behavior of the element picker so that when it is
cancelled the previously selected DOM node is re-scrolled into view.
Additionally the existing behavior of the keyboard shortcuts for the
element picker was broken when the devtools toolbox was docked. The main
content area was not being focused, so the keyboard shortcuts for the
element picker were not being used. When the toolbox is detached, the
focus event is still not fired, as it's not desirable to have the
content pop into view over the devtools.
Finally there is now an additional implementation of the Escape shortcut
when the devtools are focused. The console Escape shortcut is ignored
until the element picker has been disabled making disabling the element
picker consistent irrelevant of the context.
MozReview-Commit-ID: HxENmPBoTcD
