GDScript: Fix parsing default parameter values from function calls

modules/gdscript/tests/scripts/runtime/features/params_default_values.gd

@@ -0,0 +1,35 @@
+# https://github.com/godotengine/godot/issues/56702
+
+func test():
+	const_default()
+	func_result_default()
+	# calling again will run the initializer again,
+	# as the default is not evaluated at time of defining the function (as in python)
+	# but every time the function is called (as in C++)
+	func_result_default()
+	lots_of_defaults("non-optional")
+	# somewhat obscure feature: referencing earlier parameters
+	ref_default("non-optional", 42)
+
+
+func const_default(param=42):
+	print(param)
+
+
+var default_val := 0
+
+func get_default():
+	default_val += 1
+	return default_val
+
+
+func func_result_default(param=get_default()):
+	print(param)
+
+
+func lots_of_defaults(nondefault, one=1, two=2, three=get_default()):
+	prints(nondefault, one, two, three)
+
+
+func ref_default(nondefault1, nondefault2, defa=nondefault1, defb=nondefault2 - 1):
+	prints(nondefault1, nondefault2, defa, defb)

modules/gdscript/tests/scripts/runtime/features/params_default_values.out

@@ -0,0 +1,6 @@
+GDTEST_OK
+42
+1
+2
+non-optional 1 2 3
+non-optional 42 non-optional 41