Allow skipping of default parameters using named parameters or empty parameters (like C#)

[chucklepie]

Describe the problem or limitation you are having in your project:
Pretend you have a method like this:

func start_explosion(
		secs_alive=1.0,
		gravity=55,
                some_count=5
		showdebug=false):

Currently Godot only supports trailing default values. If you want to only override 'some_count', you have to override all of them, e.g.
start_explosion(1.0,55,1000000)

You then lose the ability to use the functions built-in default values. What would be better would be named or optional parameters, e.g.

start_explosion(some_count=100000)
start_explosion(,,,100000)

Describe the feature / enhancement and how it helps to overcome the problem or limitation:
As above

Describe how your proposal will work, with code, pseudocode, mockups, and/or diagrams:
As above

Is there a reason why this should be core and not an add-on in the asset library?:
Optional parameters are a valuable feature of modern languages and a time-saver. Otherwise, you have to resort to using dictionaries and other methods which will be more complex to implement and hinder performance in the same way.

[Calinou]

Duplicate of #1034.