Add support for GID to a tiled object.

pytiled_parser/objects.py

@@ -250,6 +250,7 @@ class _TiledObjectBase:
 
 @dataclasses.dataclass
 class _TiledObjectDefaults:
+    gid: int = None
     size: Size = Size(0, 0)
     rotation: int = 0
     opacity: float = 1

pytiled_parser/xml_parser.py

@@ -251,6 +251,11 @@ def _parse_objects(
 
         tiled_object = objects.TiledObject(id_, location)
 
+        try:
+            tiled_object.gid = int(object_element.attrib["gid"])
+        except KeyError:
+            tiled_object.gid = None
+
         try:
             width = float(object_element.attrib["width"])
         except KeyError: