Feature Request: Multiple yarn spinner projects in one app

[Person-93]

It'd be nice to be able to load multiple yarn spinner projects in one bevy app.

I'd like to have a project for each level in my game and not have to worry about nodes having the same name as nodes from other levels' scripts.

This would let me build some kind of structured story where each project has a node named Intro which runs when the level starts, Outro which runs when the level is complete, and a few other special names for significant events that happen in every level.

[Person-93]

@janhohenheim is this something you want in this library? Would you accept PRs for this?

API change

The main open question that'd need to be decided is about the default behavior of the yarn spinner plugin with no configuration and what the API of plugin type(s) should be.

I see that there is also an open issue to use yarnproject files: #118. Perhaps a good way to tackle both of these would be to make the following:

• a YarnProjectFile asset type which corresponds to a .yarnproject file (the asset loader can make it include dependencies on its yarn files). This can also hold the compiled output. (maybe in the future, the output can be a separate asset and use bevy's asset processor.)
• a YarnProject component type which includes a Handle to one of the assets
• if you want to keep the current behavior of automatically spawning the yarn project, it can be a system that handles bevy's AssetEvent and spawns an entity with a YarnProject component when a new YarnProjectFile asset is added

Internal change

The main internal code change for this would be making YarnProject a component instead of a resource and refactoring a whole bunch of things in the bevy plugin that assume there can only be one.

I think I can start working on this even if the API question is still undecided.