Called when a new train is created either through disconnecting/connecting an existing one or building a new one.
train: LuaTrainold_train_id_1?: uint32 — The first old train id when splitting/merging trains.old_train_id_2?: uint32 — The second old train id when splitting/merging trains.name: defines.events — Identifier of the eventtick: uint32 — Tick the event was generated.