Add missing REST and JSON:API test coverage for the workspace entity type

Rerolled the latest patch and turned it into a MR.

The MR is fully ready for reviews now, hiding old patches.

Using block_content json tests as references and a few other. The test coverage seems to line up with what we've done in others.

LGTM!

I looked at this two or three times and the UNCACHEABLE/MISS changes put me off committing it just yet, but... I can't think of anything else we can do here, and this is in the base class for test coverage that even the subclasses don't directly interact with, it'll make it less likely that the next entity type has to do anything special, then noticed Wim pointing out we already do the same thing elsewhere already in the test coverage. So... committed/pushed to 11.x and cherry-picked to 10.3.x, thanks!

Automatically closed - issue fixed for 2 weeks with no activity.