Support React Context API

[cbravobernal]

Fixes #38

[luisherranz]

Initial sync is working, but there are some remaining tasks:

• Make sure subscribers map is only created once
• Subscribe to block + Context, not only to Context (maybe we could use this)
• Sync initial value as well
• Check if the React warning of updating Provider during the Consumer rendering (fixed with the setTimeout at the moment) can be avoided
• Unsubscribe on the useEffect return
• Add maps or forEach in usesContext and providesContext arrays
• Investigate if using WeakMap instead of Map makes sense to avoid memory leaks

Finally, it'd be good to start thinking about how React Context should be used in the Editor.

[cbravobernal]

I'm not a memory leaks expert but, with the debug tool, it seems that using WeakMap is a better option, maybe due to its garbage collection behavior.

Without Weakmaps:

With Weakmaps

[cbravobernal]

Now the initial value is synced, by using a similar approach as the subscriber.

[cbravobernal]

If we have more than one Context in view.js files, it seems that, in the Children element, we only create the Provider the last item of the array. The code causing this issue seems to be around line 145.

In the screenshot, we can see that, on the parent component, we have CounterContext provider and ThemeContext provider, while in the child component, we only have the Counter Context.

I did a commit so anyone can test it and try to find why it happens.

[luisherranz]

This is ready now.

I've done a big refactoring of frontend.js because it was getting a bit out of hand. There will be merge conflicts in #28, but I think it was worth it.

I've also removed dprint because it was failing, and I didn't know why and I wanted to remove it anyway.