Difference and use of IfcExternalSpatialElement & IfcSpace

### Issue

The semantic difference between the use of `IfcSpace` and `IfcExternalSpatialElement` (and its tree) is not defined adaquately, and requires a wider review by the group.

### Context
we currently have a setup of 3 granularities: Facility, FacilityPart & Space. with space being the smallest representing the smallest functional area or location within a facility. this fits well with the current documentation and its original use primarily for Rooms in buildings.

But, the setup does not have any split or consideration on external or internal, with the introduction of infrastructure facilities or facility parts do not semantically define an external or internal nature, the only thing close is that an IfcBuilding is generally an enclosed structure of some sort. IfcSpace itself does not semantically define its only internal or external, its has a Pset Property to deliminate this, plus existing PDTs suchs `IfcSpaceTypeEnum.PARKING` imply the use as an external space.

in fact 90% of the `IfcSpatialStructureElement` subtypes and PDTs are external in nature making the `IfcExternalSpatialStructureElement` branch redundant.

Does anyone see a use case that would enable the substantial entity level deviation for `IfcExternalSpatialStructureElement`s

### Solutions

1. Deprecation of the current IfcExternalSpatialStructureElement branch and review/merging of the PDT's into the IfcSpaceTypeEnum.
2. Improvement to the documentation to clearly deliminate the difference and use of the concepts.