[Keyboard] Add converter/xmk (#18433)

keyboards/converter/xmk/xmk_matrix.h

@@ -0,0 +1,10 @@
+// Copyright 2022 Manna Harbour (@manna-harbour)
+// https://github.com/manna-harbour/xmk
+
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include QMK_KEYBOARD_H
+
+void xmk_matrix_key(bool press, uint8_t key);