Handle geometry collections (#476)

I was trying a clean build of RMF Demos and ran into a type error when
trying to compile maps. This PR fixes the type error. I'm not sure what
triggered it in the first place TBH.

Signed-off-by: Arjo Chakravarty <arjoc@intrinsic.ai>
Co-authored-by: Yadunund <yadunund@openrobotics.org>

rmf_building_map_tools/building_map/floor.py

@@ -141,7 +141,7 @@ def triangulate_polygon(self, polygon, triangles):
                 # to be clipped to lie within the original floor polygon
                 # for example, if a long triangle crossed a concave region
                 # and you end up with >=1 polygons and >=1 points or edges.
-                for item in geom:
+                for item in geom.geoms:
                     if item.geom_type == 'Polygon':
                         self.triangulate_polygon(item, triangles)