Meta-Thread: Enhancing Plugin/AddOn Documentation

This is a thread I create to gather issues with the documentation around Creating more Complex Editor Plugins, as a lot of it is really hidden and obscure knowledge and/or really counter-intuitive.

I will do my best to not try and tackle anything that is just about `@tool`s in general to limit the scope.

This thread is intended for me to keep track of what are available resources both inside and outside the official documentation, what are known issues that involve documentation and editors so I can brainstorm ideas for fixes.

If you want to contribute to this, feel free to drop in comments following my examples.

The permanent links:
[The branch I will be working from](https://github.com/betalars/godot-docs/tree/editor-plugin-doc-enhancements)
[Query of all issues in this repo about plugins](https://github.com/godotengine/godot-docs/issues?q=is%3Aissue%20state%3Aopen%20label%3Aarea%3Amanual%20%20(plugin%20OR%20addon))
[Query of all issues in the godot repo around documentation and plugins/extensions](https://github.com/godotengine/godot/issues?q=is%3Aissue%20state%3Aopen%20%20label%3Adocumentation%20(label%3Atopic%3Aplugin%20OR%20label%3Atopic%3Agdextension)%20)

[Root of the current Plugin Documentation](https://docs.godotengine.org/en/stable/tutorials/plugins/editor/index.html)

[This is the place where text drafts will be edited (a markdown instance hosted by a friend)](https://pad.tils.pw/RRuMpSkcSYaBHvdVFRECvA#)

No, I don't want to nessecarily solve all the issues at once, but I just want a good overview of what could use enhancement and what not.