Relocate RGB keycode processing (#7508)

* Move rgb keycode logic to process_keycode

* Fixes for rgb matrix

* Fixes for mxss

* Fix inc/dec logic, add comments

* Fix return RAINBOW_SWIRL logic

* stop external use of rgb helper functions

* merge fix

* Fix 'defined but not used' when all animations are disabled

quantum/process_keycode/process_rgb.h

@@ -0,0 +1,20 @@
+/* Copyright 2019
+ *
+ * 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 "quantum.h"
+
+bool process_rgb(const uint16_t keycode, const keyrecord_t *record);