Added IFC v4.0 json schema and added docs API for working with schemas

The schema for IFC4 the same as it was for IFC2x3.
Properties schema for IFC4 includes both quantity and propety sets.

Also cleaned up entities description for IFC2x3 from HTML code and IFC tags.

src/ifcopenshell-python/ifcopenshell/util/schema/ifc2x3_properties.json

@@ -421,9 +421,7 @@
             "SecondaryAirflowRateRange": {
                 "description": "possible range of secondary airflow that can be delivered"
             },
-            "Weight": {
-                "description": ""
-            }
+            "Weight": {}
         },
         "spec_url": "https://standards.buildingsmart.org/IFC/RELEASE/IFC2x3/TC1/HTML/psd/IfcHvacDomain/Pset_AirToAirHeatRecoveryTypeCommon.xml"
     },
@@ -5443,9 +5441,7 @@
             "HandicapAccessible": {
                 "description": "Indication whether this space (in case of e.g., a toilet) is designed to serve as an accessible space for handicapped people, e.g., for a public toilet (TRUE) or not (FALSE). This information is often used to declare the need for access for the disabled and for special design requirements of this space."
             },
-            "NetPlannedArea": {
-                "description": ""
-            },
+            "NetPlannedArea": {},
             "PubliclyAccessible": {
                 "description": "Indication whether this space (in case of e.g., a toilet) is designed to serve as a publicly accessible space, e.g., for a public toilet (TRUE) or not (FALSE)."
             },