Unify typing of variables, constants and parameters in GDScript

modules/gdscript/tests/scripts/analyzer/features/null_initializer.gd

@@ -0,0 +1,32 @@
+func check(input: int) -> bool:
+	return input == 1
+
+var recur = null
+var prop = null
+
+func check_arg(arg = null) -> void:
+	if arg != null:
+		print(check(arg))
+
+func check_recur() -> void:
+	if recur != null:
+		print(check(recur))
+	else:
+		recur = 1
+		check_recur()
+
+func test() -> void:
+	check_arg(1)
+
+	check_recur()
+
+	if prop == null:
+		set('prop', 1)
+		print(check(prop))
+		set('prop', null)
+
+	var loop = null
+	while loop != 2:
+		if loop != null:
+			print(check(loop))
+		loop = 1 if loop == null else 2