Feature request: Support folding in JSX scope

[koenpunt]

Now when folding inside a JSX scope, the parent JS scope folds instead of the JSX tags.

Not sure if this is even possible with an injection grammar(?)

[jjeising]

Can you explain how this corresponds with #14?

[koenpunt]

I opened the issue first, and then though I might be able to hook something up myself. But like I commented in #14, I think we're better of by also supporting non-default element, so that custom components can be folded as well.