Enhanced UX for surfacing who locked files better

Context

In #4623 (closed), a design proposal was made for a popover which would surface who locked files better:

Temporary development solution

To solve the immediate user need in #4623 (closed), a tooltip with the username of the user who locked the file was added in !186291 (merged) while design feedback was being iterated on.

This was not a huge priority, as the immediate user need was solved, Locking in the UI is only available for Premium/Ultimate customers, and is not heavily used.

Remaining design work

Design feedback was given to enhance the UX of this popover:

• Finish explorations for displaying lock error message inside popup &13019 (comment 2399044250)
• Explore design team feedback on lock button affordance