[Rich text editor] Provide expected DOM

[jeremie-lucca]

Front Guild is actually testing Lexical as Rich Text Editor.
They need to get a DOM to fit with Figma component.
Only requirement is to have <div contenteditable> as text section.

https://www.figma.com/design/PQEOcUF9CYfKNqaejAGLWP/Lucca-components?m=auto&node-id=6946-36388&t=QyT8rrL6aj59aR2f-1

[jeremie-lucca]

Duplicate #3253