Enum values can't be used as match patterns

[mrcdk]

Operating system or device, Godot version, GPU Model and driver (if graphics related):
Windows 10. Godot 3.0alpha1

Issue description:

Enum values can't be used as match patterns. The error is: Parse Error: Only constant expressions or variables allowed in a pattern

The match documentation says that it should be possible under the variable pattern: matches the contents of a variable/enum

Steps to reproduce:

extends Node

enum Action { Up, Down }
var current_action = Action.Up

func something():
	match current_action:
		Action.Up: # Error here
			pass
		_:
			pass

[akien-mga]

There's actually a PR already to fix that :) #10542