Feature summary:
Keyboard navigation in link input suggestion list should automatically fill the link target field.

Use case(s):
In VisualEditor, attempt to add a link. In link input, type the first letters of the page name. Press Down key to highlight a page suggestion in the list.
Expected: the input field is automatically filled with page name while browsing suggestions, so you can use it as a temporary base which you can then extend or edit.

Benefits:
This behavior would be consistent with how browser URL bar do work.
This would also allow to get page section suggestions (T52881) quickly, without typing manually the whole page name.