Use "filled" bookmark icon when the item is bookmarked (#38239)

* Use "filled" bookmark icon when the item is bookmarked

* Update E2E tests

* Update the affected unit test

* Make dashboard header icons smaller and darker

* Make dashboard bookmark icon look like its neighbors

* Unify question and dashboard icon's background on hover

Question icons have been using `text-medium` unlike dashboard icons
that had `text-light`.