ElevatorSim output is not initially valid (until update has been called)

[chauser]

Describe the bug
Immediately after creating an ElevatorSim with non-zero starting position, a call to getPositionInMeters returns 0. I have not investigated whether other mechanism Sim classes are also affected. The problem may be even more general in that ElevatorSim uses LinearSystemSim.setState to put the starting position into the state, but setState does not update the Y matrix (outputs) to correspond. It is unclear to me whether it would be desirable (or even possible) for it to do so.

To Reproduce

       LinearSystem<N2, N1, N2> elsys = LinearSystemId.createElevatorSystem(
            DCMotor.getFalcon500(2), 
            4.0, 
            0.02, 
            9.0);
            
        // the only thing here that is essential for illustrating the behavior is that the field containing -0.05 is non-zero.
        ElevatorSim m_elevatorSim = new ElevatorSim(
            elsys,
            DCMotor.getFalcon500(2),
            0.0,
            1.15,
            true,
            -0.05
        );

        double initialPos = m_elevatorSim.getPositionMeters();

Observe initialPos is 0.0 when it should be -0.05.

Expected behavior
Calling getPositionInMeters returns the correct position at all times after construction. If that is not possible then the behavior should be documented (though that is much less desirable in my opinion).

• Project Information:
  WPILib Information:
  Project Version: 2025.2.1
  VS Code Version: 1.94.2
  WPILib Extension Version: 2025.2.1
  C++ Extension Version: 1.23.2
  Java Extension Version: 1.38.0
  Java Debug Extension Version: 0.58.2024090204
  Java Dependencies Extension Version 0.24.1
  Java Version: 17
  Java Location: /home/hauser/wpilib/2025/jdk
  Vendor Libraries:
  PathplannerLib (2025.2.1)
  CTRE-Phoenix (v5) (5.35.1)
  CTRE-Phoenix (v6) (25.2.1)
  REVLib (2025.0.2)
  ReduxLib (2025.0.1)
  Studica (2025.0.1)
  ThriftyLib (2025.0.1)
  WPILib-New-Commands (1.0.0)
  maplesim (0.3.1)
  photonlib (v2025.1.1)

Additional context
Workaround: call update on the ElevatorSim object immediately after construction.

[calcmogul]

Yea, we could just call the measurement model in the constructor of all the sim physics classes. We may need to add that to setState() to maintain the invariant that the state and measurement match up.