Enable LocalEntitiesInstanceProvider only if a form uses entities

[grzesiek2010]

Closes #6425

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[grzesiek2010]

At first, the issue seemed pretty straightforward based on the description, but it turned out to be more complex.

In Javarosa, choices are loaded without any awareness of entities - it treats all choices the same way. I believe that was intentional, and we don’t want to change this by passing the usesEntities parameter into Javarosa.

In Collect, we have LocalEntitiesInstanceProvider, which Javarosa uses to load entities (instead of choices from a static CSV file) when a matching dataset exists (as described in the issue). However, at that point we don’t have any details about the form (whether it uses entities or not) that could help us decide whether LocalEntitiesInstanceProvider#isSupported should return true or false.

Given that, the simplest solution I can think of is to introduce something similar to what we did for enabling/disabling entities in the settings. There, we had a function that determined whether LocalEntitiesInstanceProvider should be added. The difference now would be that instead of checking the settings (like before), the function would check the currently loaded form.

What do you think about this approach @seadowg?

[seadowg]

I've realized that I don't think this entirely solves the problem sadly: you could still have a form that uses an entity list, but also has a non entity list CSV that clashes with an entity list in the project. That's definitely an edge case, but I think the flow in the issue is as well.

I think to fully solve this we really need to be able to have access to information about the media file we're referencing (through a MediaFileRepository) for example. This is something that we've talked about on and off, but it's always been hard to justify. Maybe we should bite the bullet here? This could be a good issue to drive that out.