Bug: collapsible container is not being exported faithfully to markdown/html

[vadimkantorov]

For some blocks, peppering markdown with some html is required or desirable to preserve semantics or visuals.

E.g. for collapsible container:

currently is exported as

How it is typically done in markdown documents on GitHub:

<details><summary>
hello
</summary>

world
</details>

Rendered:

hello

world

---

Without HTML, it could at least be exported as:

**hello**
---
world

In general, it is important in many practical usecases to at least optionally (behind some option) add some minimal HTML tags to preserve semantics during Markdown export. E.g. for image/text centering as we discussed in:

• https://github.com/facebook/lexical/issues/6325#issuecomment-2184220501

[vadimkantorov]

Maybe this issue is duplicate of:

• https://github.com/facebook/lexical/issues/4355

The advantage of this dup is that it has some playground screenshots :)