Improve "choose from library" workflow to be clear about published content only [NEEDS UX]

[bradenmacdonald]

Currently, it's confusing for users that a different set of content is shown in the "Library Content Picker" modal than in the libraries UI:

It's jarring to be looking at a view of content with the recently modified sort in the library, and the same sort from the course displays a different content set.

For now we have a minimal workaround via #1485 but this may need a significant re-think in terms of the overall flow and UX.

Some ideas for this were discussed in this Slack thread

e.g. display unpublished content as "ghost" that can be insta-published from the picker modal:

e.g. forcing on the published filter from #1484