Add Input action autocompletion for user define function

[Brahmbir]

similar to Input.is_action_just_released() and other inbuild methods similar to this one. Godot will autocomplete with the input filled according to the project's settings.

but not in user define function

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

add a comment tag for functions
like in jsdoc

 ##  brief description
 ## @param {Action} action
func funcOnAction(action:StringName) :
       pass 

When adding a node to a group, Godot will remember the names and save them in the .godot directory. By doing so, when using group methods, it will be able to autocomplete the group's name in the editor.

#If this enhancement will not be used often, can it be worked around with a few lines of script?
I think it will be useful for everyone but I don't know if it can be done using an addon.

#Is there a reason why this should be core and not an add-on in the asset library?
i think it is important as it useful in example of key remapping , so more developers can benefit from it.

[dalexeev]

I don't think it's a good idea to use doc comment tags for this purpose. I don't like that PHP for example has essentially a second type system in doc comments. If we wanted to introduce optional type annotations, I would prefer the Python option. But in GDScript we already have optional type hints with runtime checks.

As for autocompletion, I think the most optimal solution would be to expose the get_argument_options() method. See #10972.

Currently, you can implement an editor plugin, example. But this is not a very convenient option, since for better support you would need to implement a GDScript parser. However, in practice, you can use a regexp-based approach for basic scenarios.