Refactor: Rename OB_GPENCIL and ID_GD

This renames the `OB_GPENCIL` object type and the `ID_GD` to `OB_GPENCIL_LEGACY` and `ID_GD_LEGACY` respectively.
There is no change for the user.

Pull Request: blender/blender#105541

source/blender/io/collada/SceneExporter.cpp

@@ -46,7 +46,7 @@ void SceneExporter::exportHierarchy()
         case OB_CAMERA:
         case OB_LAMP:
         case OB_EMPTY:
-        case OB_GPENCIL:
+        case OB_GPENCIL_LEGACY:
         case OB_ARMATURE:
           base_objects.add(ob);
           break;