c49bc7c7c0
Add a warning in user_model.cc if a flex is not rigid and has no edge equality constraints or passive forces (edge stiffness, edge damping, or vertex damping). Such flexes would not affect the simulation. A test case is added to verify the warning. PiperOrigin-RevId: 889215981 Change-Id: I481128e1456921b632719547c676d201fdfbe931