Make the method selector dialog available via EditorInterface

[ydeltastar]

We can select object properties with EditorInterface.popup_property_selector but there is no equivalent to select methods. This PR adds EditorInterface.popup_method_selector so we can use the method selector dialog.

@tool
extends EditorScript


func _run() -> void:
	EditorInterface.popup_method_selector(self, _method_selector, "_run")


static func _method_selector(method_name: String):
	print("Method: %s" % method_name)