[DOCS] Add a tutorial series on translating between engine and script code.

[willnationsdev]

Go through an example of taking a complex Engine class (or set of classes) and walk through how to change it into script code. Illustrates relationship between engine/script code and teaches people how to build their own complex objects. Going to use EditorInspector to teach people how to build their own editor (slightly).

Go through an example of taking a scene one has built in the editor and converting it into an engine module. Scene -> Script -> C++ class.

[willnationsdev]

In the process of creating these docs, I will have created a script-based foundation for a user's own Inspector. Once this foundation is in place and integrated into godot-next, contributors can then begin creating specific Property GUI implementations, like EditorProperty, but not tied directly to the editor.

[willnationsdev]

This proved to be very involved so I have the branch, but I will likely be focusing (for now anyway) on other tasks.