Proposal to clarify how cranes are classified in IfcTransportElement

Cranes are really important.

Cranes don't have an obvious classification. The closest is IfcTransportElement, perhaps using the weird enum value of "LIFTINGGEAR". Brought up [here](https://forums.buildingsmart.org/t/what-ifcproduct-subtype-should-be-considered-for-cranes-tower-crane-specifically/2667/3) but something I struggle with very often at work.

One of the key decisions in construction is what type of crane, how many, and where. Cranes may include crawler cranes, mobile cranes, hammerhead, luffing, and probably more. I can find a domain expert to give me a list if necessary.

Option 1: Add a "CRANE" enum. Distinguish it in the enum description, especially from craneway which is more like a gantry from my understanding.

Option 2: Add a lot of crane enums. "CRAWLERCRANE" "TOWERCRANE" "MOBILECRANE". Probably get a list from a expert :)

Option 3: Add a subclass IfcCrane. After all IfcTransportElement seems to be meant for what in Australia we'd call the Vertical Transportation consultant (escalators, lifts, disabled access lifts, travellators, etc). It's a very different domain and may be preferred if IFC wants to easily capture 4D stuff. Right now, there are a whole series of stuff which just doesn't have a nice home - they exist in IfcConstructionEquipmentResource but not as actual products on site with geometry (and geometry is crucial). Stuff like hoists, scaffolding, cranes, concrete pump trucks, and hoarding.

Start by reading the existing IfcTransportElement classification and the linked forum discussion about crane subtypes. Compare the CRANE enum, detailed crane enums, and IfcCrane alternatives with the existing IfcConstructionEquipmentResource scope; done requires an agreed classification direction and documented treatment for cranes and related equipment.

Written by the indexing model from the issue text.