[3.x] Code completion is not full for custom functions

[smedelyan]

Godot version: 3.1

OS/device including version: Ubuntu 18.04

Issue description:
Code completion does not provide parameter hints for custom functions if they are used from a script other than they are declared in.

# one script
extends Object
class_name KnownClass

func test(param: String):
	pass

# another script
extends Node2D

func _ready():
	var kc: KnownClass = KnownClass.new()
	kc.test("here completion does not show parameter list")

Minimal reproduction project:
repro_cc_custom_func.tar.gz

[Ranoller]

You are right, i can confirm that.... but from long ago. And it´s not consistent, some times code completion doesn´t provide parameters of script self functions once "(" character is reached. And sometimes doesn´t provide autocompletion for self script functions at all.

[smedelyan]

@Ranoller then the time has come to finally solve this annoying one! =)

[KoBeWi]

Still happens in ae21b5d
Probably worth to check again after GDScript rewrite.

[HolonProduction]

Does not apply to 4.x