Add IsGroupedBy in function get_decomposition (#2513)

* Add IsGroupedBy in function get_decomposition

selector example : "@ .IfcZone & .IfcSpace"

* Update element.py

* Change name function get_group

get_group to get_grouped_by

src/ifcopenshell-python/ifcopenshell/util/element.py

@@ -376,7 +376,27 @@ def get_decomposition(element):
             results.append(rel.RelatedBuildingElement)
     return results
 
+def get_grouped_by(element):
+    """
+    Retrieves all subelements of an element based on the group.
 
+    :param element: The IFC element
+    :return: All subelements of the group
+
+    Example::
+
+        element = file.by_type("IfcGroup")[0]
+        subelements = ifcopenshell.util.element.get_group(element)
+    """
+    queue = [element]
+    results = []
+    while queue:
+        element = queue.pop()
+        for rel in getattr(element, "IsGroupedBy", []):
+            queue.extend(rel.RelatedObjects)
+            results.extend(rel.RelatedObjects)
+    return results
+    
 def get_aggregate(element):
     """
     Retrieves the aggregate of an element.