small optimization for da1bdc8

On large projects predict dense mesh stage can take 20s+ and reusing attribute value can save up to half of this time.
Using indices also helps but it's not that significant and sometimes it's the same time as using attribute names.

src/blenderbim/blenderbim/bim/import_ifc.py

@@ -609,20 +609,23 @@ def predict_dense_mesh(self):
         threshold = 10000  # Just from experience.
 
         # The check for CfsFaces/Faces/CoordIndex accommodates invalid data from Cadwork
-        faces = [len(e.CfsFaces) for e in self.file.by_type("IfcClosedShell") if e.CfsFaces]
+        # 0 IfcClosedShell.CfsFaces
+        faces = [len(faces) for e in self.file.by_type("IfcClosedShell") if (faces := e[0])]
         if faces and max(faces) > threshold:
             self.ifc_import_settings.should_use_native_meshes = True
             return
 
         if self.file.schema == "IFC2X3":
             return
 
-        faces = [len(e.Faces) for e in self.file.by_type("IfcPolygonalFaceSet") if e.Faces]
+        # 2 IfcPolygonalFaceSet.Faces
+        faces = [len(faces) for e in self.file.by_type("IfcPolygonalFaceSet") if (faces := e[2])]
         if faces and max(faces) > threshold:
             self.ifc_import_settings.should_use_native_meshes = True
             return
 
-        faces = [len(e.CoordIndex) for e in self.file.by_type("IfcTriangulatedFaceSet") if e.CoordIndex]
+        # 3 IfcTriangulatedFaceSet.CoordIndex
+        faces = [len(index) for e in self.file.by_type("IfcTriangulatedFaceSet") if (index := e[3])]
         if faces and max(faces) > threshold:
             self.ifc_import_settings.should_use_native_meshes = True