Add nodes for creating note arrays in-editor.

rhythm_game/note/editor/editor_note_array.gd

@@ -0,0 +1,10 @@
+class_name EditorNoteArray extends NoteArray
+
+func _ready() -> void:
+	for note: EditorNote in get_children():
+		if note == null:
+			return
+		# TODO: Make this insert sorted.
+		_beats.append(note.hit_beat)
+		_types.append(note.type)
+		_lanes.append(note.lane)