feat: add after queued renders promises to render management

[BeksOmega]

The basics

• I branched from develop
• My pull request is against develop
• My code follows the style guide
• I ran npm run format and npm run lint

The details

Resolves

Fixes #6978

Proposed Changes

Adds a promise to the render management system that is resolved when all queued renders have completed.

Reason for Changes

Allows extra behavior to be tacked on to the end of rendering (useful for things that need updated positioning / size information for blocks).

Test Coverage

Added tests that the promise is actually resolved.

Documentation

N/A, but related to #6980

Additional Information

We are now exporting the render management system (which only exports the afterQueuedRenders function. I exported this because (as Maribeth discovered) elements on the widget div will need to delay repositioning until after rendering. And we do allow external developers to add elements to the widget div.

Also modifies the insertion marker manager to actually use the promise. Manually verified that it works as expected.

[maribethb]

overall i think this approach is more readable, thanks for updating it.

i'm still not totally sold on the name of this function but i haven't come up with anything that's better so feel free to submit but here's some ideas in case any of them conjure up anything good for you

queuedRenders
waitForQueuedRenders
rendersInProgress
doRenders
doQueuedRenders

etc. I think the reason I don't like it is after implies the work that is done "after" the current renders, but that's not what is returned by this function. The work that is done "after" the current renders is actually whatever is passed to the then that will follow this function call. So I am trying to find a name that makes this function refer to the actual queued renders themselves, while not being misleading into making you think calling this function will actually kick off a new render cycle. I don't think I've succeeded there.

So I know doRenders is already the name of a function but for example doQueuedRenders().then(doMoreWork) reads better to me than afterQueuedRenders().then(doMoreWork) because the latter makes it sound like there is some other work that is after the queued renders that we're waiting on, and I wonder how I sign up to add work to that.

So basically I'm probably overthinking it and this is approved, but I'll check one more time if you have any better naming ideas than I did...

[BeksOmega]

Discussed offline and went with finishQueuedRenders.

Works pretty well as both await finishQueuedRenders() and finishQueuedRenders().then(). Also communicates that there's already some work being done, and that we are waiting until the end of it :D