Reduce the number of ways to convert Lexical <-> HTML

[GermanJablo]

There are currently 4 ways to convert from Lexical to HTML and vice versa. This is a huge problem for DX because it means that every user creating a node has to maintain 4 up-to-date and consistent serializations. And this is not even counting other forms of serialization required in Lexical, such as JSON or Markdown.

An example of the disadvantages of this is #9165, which would not have been necessary because that bug had already been solved in Lexical: facebook/lexical#6693, but we are not using their HTML converter.

Our goal is to reduce as many of these alternative serializations as possible.

Strategy	By	Notes
1. $generateHtmlFromNodes and $generateNodesFromDOM	Lexical
2. LexicalNode.createDOM and DecoratorNode.decorate Lexical	Lexical
3. Jsx custom serializer	Payload	The custom JSX serializer is used for things like Live Preview, or for rendering on the website. Basically the same as (2), but doesn't require importing Lexical or nodes. Is it worth it?
4. convertLexicalToHTML	Payload	This has no advantage over (1), so it has no reason to exist.

Recommendations:

• Make (4) convertLexicalToHTML rely on (1) $generateHtmlFromNodes.

• We cannot remove the current way of converting to HTML for backwards compatibility, but we can promote the new way in the documentation.

• Replace the places where we are using (3) with (1/4) instead. HTML should work fine. The cases where someone might want JSX are rare exceptions. The only examples I can think of are:

  • Next.js Link
  • Stateful components that do not require persistence
    These cases seem rare enough that we could focus on (1/4), with the guidance: "If you need complex rendering, consider instantiating Lexical or develop a custom JSX serializer."

  Also, at one point I considered using just (3), and building a static HTML similar to (1/4) using ReactDOMServer.renderToString. I actually have a prototype in the serialize-jsx-html branch, but I'm not sure if it's worth it, given that Lexical already provides HTMLConverters that work for 99% of cases.