Move more dungeon parameter selection to mapgens (#8653)

Move more dungeon parameter selection to mapgens (#8653)

Move 'num_dungeons' to 'DungeonParams'.
Add new parameter 'num_rooms' to replace 'rooms_min' and 'rooms_max',
so that the mapgen has complete control over the number of rooms.
Add new bool 'first_room_large' so that the mapgen chooses this
instead of a hardcoded 1 in 4 chance.
Add new parameter 'room_size_large' to replace 'room_size_large_min'
and 'room_size_large_max', so that the mapgen has complete control
over this.