fix(split): Add define for local source.

* Add `ZMK_POSITION_STATE_CHANGE_SOURCE_LOCAL` and use
  it consinstently to fix bug w/ local `&reset`, `&bootloader`, etc.

app/include/zmk/events/position_state_changed.h

@@ -9,6 +9,8 @@
 #include <zephyr.h>
 #include <zmk/event_manager.h>
 
+#define ZMK_POSITION_STATE_CHANGE_SOURCE_LOCAL UINT8_MAX
+
 struct zmk_position_state_changed {
     uint8_t source;
     uint32_t position;

app/src/keymap.c

@@ -207,7 +207,7 @@ int zmk_keymap_apply_position_state(uint8_t source, int layer, uint32_t position
         return invoke_locally(&binding, event, pressed);
     case BEHAVIOR_LOCALITY_EVENT_SOURCE:
 #if ZMK_BLE_IS_CENTRAL
-        if (source == UINT_MAX) {
+        if (source == ZMK_POSITION_STATE_CHANGE_SOURCE_LOCAL) {
             return invoke_locally(&binding, event, pressed);
         } else {
             return zmk_split_bt_invoke_behavior(source, &binding, event, pressed);

app/src/kscan.c

@@ -51,7 +51,7 @@ void zmk_kscan_process_msgq(struct k_work *item) {
         LOG_DBG("Row: %d, col: %d, position: %d, pressed: %s", ev.row, ev.column, position,
                 (pressed ? "true" : "false"));
         ZMK_EVENT_RAISE(new_zmk_position_state_changed(
-            (struct zmk_position_state_changed){.source = UINT8_MAX,
+            (struct zmk_position_state_changed){.source = ZMK_POSITION_STATE_CHANGE_SOURCE_LOCAL,
                                                 .state = pressed,
                                                 .position = position,
                                                 .timestamp = k_uptime_get()}));