More involved Text Editor interface with buttons for BBCode

### Describe the feature / enhancement and how it helps to overcome the problem or limitation

Very similar to what you get when you write anything on Github:

Have buttons for every known [bbcode option](https://docs.godotengine.org/en/stable/tutorials/gui/bbcode_in_richtextlabel.html), plus elegant support for [custom effects](https://docs.godotengine.org/en/stable/tutorials/gui/bbcode_in_richtextlabel.html#custom-bbcode-tags-and-text-effects) in the future.

Additionally, there could be syntax highlighting for the text editor to color bbcode tags less intrusively, and apply their effects during editing, similar to how Discord markdown applies itself mid-typing:

This was actually previously achieved by [@fantoser ](https://github.com/Fantoser/) as a proof of concept but on the old pre-event system version: