Add Support for USB programmable buttons (#12950)

quantum/process_keycode/process_programmable_button.h

@@ -0,0 +1,23 @@
+/*
+Copyright 2021 Thomas Weißschuh <thomas@t-8ch.de>
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#pragma once
+
+#include <stdint.h>
+#include "quantum.h"
+
+bool process_programmable_button(uint16_t keycode, keyrecord_t *record);