Editor: Fixed SetGeometryCommand failed to UNDO/REDO

[ycw]

Related issue: #28345 ( issue 2 )

Issue: SetGeometryCommand failed to UNDO/REDO

Because it wrongly serializes oldGeometry as current object's geometry.

To reproduce:

1. Go to https://threejs.org/editor/
2. In SETTINGS tab, enable persistent in History section
3. Add a Box
4. Select Box in outliner, then in GEOMETRY tab, update Width from 1 to 2
5. Refresh the page
6. Press Edit>Undo
7. You should see the box's width is of 2, not 1

Solution (This PR)

Fixed that by serializing the this.oldGeometry.toJSON() instead