To properly retrigger hold-taps when a combo is not activated, some
position down events are reraised instead of released. The corresponding
position up events were never reraised, causing a potential stuck key.
* Make it easier to use *just* event payloads by defining the data,
and then having event manager macros generate "wrapper structs"
* Improve is_*/cast_* APIs to hide details of full event struct.
* Create `zmk_event_t` typedef to pass to event handlers.
* Bring event names inline w/ consistent `zmk_` prefix.
