Admin Bar: Can't open edit dropdown with a keyboard

[ryelle]

It appears that the 'Edit' options are no longer accessible from the keyboard since this change. @alexstine, the Make/Accessibility team rep noted this because it significantly broke his workflow to not be able to reach the 'Edit Post' submenu while posting agendas & meeting notes.

I haven't explored thoroughly, but I think it broke the event handlers in /js/_enqueus/lib/admin-bar.js

From #256 (comment)

The top-level edit "link" is not a link, so it doesn't get focus, which means the submenu can't open via keyboard. "Edit [object]" is a common use, so this should probably go back to being a top-level item anyway (see #271).