Units::teleport does not correctly handle Wagons

[quietust]

The gui/teleport script uses the Units::teleport(df::unit *, df::coord) function to move units, and it appears to be capable of teleporting caravan wagons. However, it does not have the necessary logic to adjust occupancy flags for EQUIPMENT creatures, which means it will leave the map's occupancy flags in an inconsistent state afterwards.

DF's own functions unitst::do_largeocc() and unitst::undo_largeocc() are responsible for handling this.

[Alistair-Afton]

Confirmed. Units::teleport only updates the unit/unit_grounded occupancy bits on the single center tile, so EQUIPMENT-sized units like wagons leave stale flags on the other tiles of their footprint and arrive with none set.

unitst::do_largeocc/undo_largeocc are not mapped in df-structures yet, so the fix either needs those added to symbols, or teleport needs to replicate the footprint update itself (which we would want to verify against a live wagon, since the footprint logic lives in those functions).

[Alistair-Afton]

Fix in #5924. Rather than mapping do_largeocc/undo_largeocc (which would need per-platform symbol work), teleport now derives the footprint extent from the race's EQUIPMENT_WAGON flag and applies the same occupancy update across all 9 tiles. Verified live: all source tiles clear and all destination tiles set on teleport, and ordinary units keep single-tile behavior.