[Keyboard] Add LAYOUT_60_iso to XD60 (#7263)

* refactor iso keymap

- remove redundant action_layer.h include
- use enum for layer management
- QMK coding conventions (four-space indent)

* add LAYOUT_60_iso macro

* enable 60_iso community layout for both revisions

* swap KC_HOME to KC_RSFT

* update ISO keymap readme

* update default keymap readme

`make` command no longer valid.

* refactor keyboard readme

Update to reflect current QMK template.

* add LAYOUT_60_iso data to info.json

* use #pragma once in header files

keyboards/xd60/rev2/config.h

@@ -15,8 +15,7 @@ You should have received a copy of the GNU General Public License
 along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
 
-#ifndef CONFIG_H
-#define CONFIG_H
+#pragma once
 
 #include "config_common.h"
 
@@ -70,5 +69,3 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
 #define LOCKING_SUPPORT_ENABLE
 /* Locking resynchronize hack */
 #define LOCKING_RESYNC_ENABLE
-
-#endif