unhardcode StTempleFall and add a trigger

### I am planning on implementing this myself

Yes

### Describe your request

currently, the temple fall 'cutscene' is only triggered by the `NPC05_Badeline` cutscene, and therefore to the room `c-00`; the y-coordinate that triggers it and the x-coordinate the player floats to are hardcoded.
as several people have requested being able to use `StTempleFall` in custom maps, and this is currently very hard as it requires recreating the state from scratch in a lua cutscene, it would be nice if an `everest/templeFallTrigger` was added.