Model.WorldPivotData does not need a custom setter/getter and should instead alias to Model.WorldPivot

[Dekkonot]

As it says in the issue title, right now we have a custom setter/getter for Model.WorldPivotData in rbx_dom_lua that just sets Model.WorldPivot directly. This is correct behavior, but it's also unnecessary and we should instead alias WorldPivotData.

This is complicated somewhat because they're two different types (WorldPivotData is OptionalCFrame, WorldPivot is CFrame) but we can add a conversion between the two and then set an alias.