Fullscreen / Focus Mode for richtext editor

[midnightgrocer]

What

Add a toggle to enter fullscreen / immersive / focus mode for the richtext editor.

Why

Currently the editing experience can feel a bit cramped and distracting, especially for non-technical editors. The flexibility of Lexical is a big selling point to make dynamic documents and it would be cool to be able to take full advantage of the screen real estate to craft those documents and focus up.

Example

A toggle over the lexical editor toolbar would be a straightforward approach as pictured below, but there might also be an opportunity to bring the "focus" mode to a higher layer. For instance, maybe Content, Meta, and SEO should be included as tabs in the fullscreen mode in which case you may want to reposition the fullscreen toggle to a nearby area and not on the lexical toolbar.