feat: added heading jsx provider

[AdrianMaj]

Hey, I added JSX provider for H1-H6 headings. I use it in my project, and didn't see a ready version, so here it is.

[rubn-g]

Thanks for your contribution! Lexical creates a text node type inside heading node for colored text, so this converter shouldn't be required, that's also how bold, italic, and other formatting options, works. So text JSX converter should cover this use case too.

I tested changing colors of a heading and lexical created the text node inside the heading node, as expected. Did you find any case where lexical didn't create a text node for color styling?

[AdrianMaj]

@rubn-g Yeah, I got unknown-node text instead of heading without that. One thing to mention is that I use only selected content from repo, as whole package triggers me an Couldn't resolve 'fs' error

[rubn-g]

We should fix the Couldn't resolve 'fs' error then and this Heading JSX converter, won't be required to achieve what we want.
I'll try to fix that error

[AdrianMaj]

It's some problem with npm package, as source code works well