Begin to carve out platform/protocol API - Single main loop (#13843)

* Begin to carve out platform/protocol API

* Fix up after rebase

quantum/main.c

@@ -0,0 +1,41 @@
+/* Copyright 2021 QMK
+ *
+ * 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 3 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/>.
+ */
+
+#include "keyboard.h"
+
+void platform_setup(void);
+
+void protocol_setup(void);
+void protocol_init(void);
+void protocol_task(void);
+
+/** \brief Main
+ *
+ * FIXME: Needs doc
+ */
+int main(void) __attribute__((weak));
+int main(void) {
+    platform_setup();
+    protocol_setup();
+
+    protocol_init();
+
+    /* Main loop */
+    while (true) {
+        protocol_task();
+        housekeeping_task();
+    }
+}