Improve distinction between known / potential GMF labels in the UI

[npit]

I think the GMF annotation UI could be improved by making the known / potential fields more visually distinct.
E.g. here's the "goals" section: currently

You currently have to read the labels / count the number of text inputs to figure out
which GMF section you're adding labels to. I was wondering of a visual hint (styling / "?" symbol / ...)
to designate the difference would be useful.

I understand that I'm probably overreacting ("the UI is expecting me to read?! outrageous!"),
so I'm preemptively adding a low-priority tag 😛 . It did confuse me enough to lead to #2686 , however.