Add a toggle key for GUI On/Off in Magic feature (qmk#13830)

Author: drashna

docs/keycodes_magic.md

@@ -24,6 +24,7 @@
 |`MAGIC_TOGGLE_ALT_GUI`            |`AG_TOGG`|Toggle Alt and GUI swap on both sides                                     |
 |`MAGIC_NO_GUI`                    |`GUI_OFF`|Disable the GUI keys                                                      |
 |`MAGIC_UNNO_GUI`                  |`GUI_ON` |Enable the GUI keys                                                       |
+|`MAGIC_TOGGLE_GUI`                |`GUI_TOG`|Toggles the status of the GUI keys                                        |
 |`MAGIC_SWAP_GRAVE_ESC`            |`GE_SWAP`|Swap <code>&#96;</code> and Escape                                        |
 |`MAGIC_UNSWAP_GRAVE_ESC`          |`GE_NORM`|Unswap <code>&#96;</code> and Escape                                      |
 |`MAGIC_SWAP_BACKSLASH_BACKSPACE`  |`BS_SWAP`|Swap `\` and Backspace                                                    |

quantum/process_keycode/process_magic.c

@@ -164,6 +164,9 @@ bool process_magic(uint16_t keycode, keyrecord_t *record) {
                     case MAGIC_EE_HANDS_RIGHT:
                         eeconfig_update_handedness(false);
                         break;
+                    case MAGIC_TOGGLE_GUI:
+                        keymap_config.no_gui = !keymap_config.no_gui;
+                        break;
                 }
 
                 eeconfig_update_keymap(keymap_config.raw);

quantum/quantum_keycodes.h

@@ -521,6 +521,9 @@ enum quantum_keycodes {
     KEY_OVERRIDE_ON,
     KEY_OVERRIDE_OFF,
 
+    // Additional magic key
+    MAGIC_TOGGLE_GUI,
+
     // Start of custom keycode range for keyboards and keymaps - always leave at the end
     SAFE_RANGE
 };
@@ -694,6 +697,7 @@ enum quantum_keycodes {
 
 #define GUI_OFF MAGIC_NO_GUI
 #define GUI_ON MAGIC_UNNO_GUI
+#define GUI_TOG MAGIC_TOGGLE_GUI
 
 #define GE_SWAP MAGIC_SWAP_GRAVE_ESC
 #define GE_NORM MAGIC_UNSWAP_GRAVE_ESC