Display quick documentation with code completion hints in the script editor

[ghost]

Describe the project you are working on:
Experimenting with using Visual Studio Code as external editor.

Describe the problem or limitation you are having in your project:
Using Visual Studio Code as the auto-completion hints describe what a function does rather than just display a list of functions to choose from which is how the Godot editor behaves currently.

Describe the feature / enhancement and how it helps to overcome the problem or limitation:
Especially when you can't remember what a function is supposed to do, yes you can look it up in the documentation, however it would be more convenient to have the auto-completion hints text showing, similar to the godot-tools extension does in Visual Studio Code. This will make the experience of using the internal editor better.

Describe how your proposal will work, with code, pseudocode, mockups, and/or diagrams:
For each function that appears in the auto-complete dropdown, full hints are displayed. This would be derived from the Godot documentation which is how the godot-tools is working.

If this enhancement will not be used often, can it be worked around with a few lines of script?:
No. The only alternative is to use the external editor, however the suggestion is about making the experience using the internal editor better.

Is there a reason why this should be core and not an add-on in the asset library?:
This is an editor enhancement.

[Calinou]

Duplicate of #408.