feature wish: highlight the corresponding hyp in the goals buffer when completing.

[Matafou]

Hi there,
when completing a hypothesis name and scrolling in the completion popup menu, it would be nice to have the selected hypothesis be highlighted in the goals buffer. So that we can see its type.
Ideally the other names of the popup would also be highlighted but less visibly.
Note sure if I am able to propose a PR for that though.
Best