Godot version:
3.2.2 Beta 1 Mono

OS/device including version:
Linux Mint 19.3

Issue description:

Since all scripts should be compatible with each other, GDScript should be able to extend C# Scripts.

For example:

class MyMonoScript : Node
{
    public void ComplexLogic()
    {
    }
}

extends MyMonoScript
func _ready():
    ComplexLogic()

An example of how this may be used is a World.cs file with logic that a GDScript file can inherit so that custom worlds can be made with a single GDScript file

Steps to reproduce:

• Make a C# Script
• Make a GDScript that inherits that C# Script

Minimal reproduction project:
Test.zip