Make hover cards interactive

[matthew-white]

Right now, it's not possible to hover over a hover card (or at least it's not meant to be possible). As soon as you hover away from the element that showed the hover card, even if it's to mouse into the hover card, that will have the effect of hiding the hover card. However, there could be benefits in allowing the user to mouse into hover cards:

• Users could see tooltips over truncated text.
• Scrolling through the list of entity properties
• Linking (e.g., from the hover card for a submission to the listed form)
• Users would be able to select and copy text shown in the hover card.

@sadiqkhoja suggested this idea during code review: getodk/central-frontend#1067 (comment)

issa wrote about this idea on Slack:

we can upgrade them to be interactive someday