race condition between oneshot_mods and tap_dance

since the keycode for a tap dance process gets process only after the
TAPPING_TERM timeout, you really only have ONESHOT_TIMEOUT -
TAPPING_TERM time to tap or double tap on the key. This fix save the
oneshot_mods into the action.state structure and applies the mods with
the keycode when it's registered. It also unregisters the mod when the
the tap dance process gets reset.

quantum/process_keycode/process_tap_dance.c

@@ -43,12 +43,16 @@ static inline void process_tap_dance_action_on_dance_finished (qk_tap_dance_acti
   if (action->state.finished)
     return;
   action->state.finished = true;
+  add_mods(action->state.oneshot_mods);
+  send_keyboard_report();
   _process_tap_dance_action_fn (&action->state, action->user_data, action->fn.on_dance_finished);
 }
 
 static inline void process_tap_dance_action_on_reset (qk_tap_dance_action_t *action)
 {
   _process_tap_dance_action_fn (&action->state, action->user_data, action->fn.on_reset);
+  del_mods(action->state.oneshot_mods);
+  send_keyboard_report();
 }
 
 bool process_tap_dance(uint16_t keycode, keyrecord_t *record) {
@@ -70,6 +74,7 @@ bool process_tap_dance(uint16_t keycode, keyrecord_t *record) {
       action->state.keycode = keycode;
       action->state.count++;
       action->state.timer = timer_read();
+      action->state.oneshot_mods = get_oneshot_mods();
       process_tap_dance_action_on_each_tap (action);
 
       if (last_td && last_td != keycode) {

quantum/process_keycode/process_tap_dance.h

@@ -9,6 +9,7 @@
 typedef struct
 {
   uint8_t count;
+  uint8_t oneshot_mods;
   uint16_t keycode;
   uint16_t timer;
   bool interrupted;