Experimental get_inverse_cardinality proposal. See #1904.

src/ifcopenshell-python/ifcopenshell/file.py

@@ -391,6 +391,16 @@ class file(object):
             return inverses
         return set(inverses)
 
+    def get_inverse_cardinality(self, inst):
+        """Returns the number of entities that reference this entity
+
+        :param inst: The entity instance to get inverse relationships
+        :type inst: ifcopenshell.entity_instance.entity_instance
+        :returns: 0 if no references, 1 if one reference, or 2 if more than one reference
+        :rtype: int
+        """
+        return self.wrapped_data.get_inverse_cardinality(inst.wrapped_data)
+
     def remove(self, inst):
         """Deletes an IFC object in the file.