[wpilib] Simulation: Add ctor parameter to set starting state of mechanism sims (#5288)

- Add a constructor parameter to configure the initial angle of the arm
- Also reorganizes cascading constructors for Java

wpilibcExamples/src/main/cpp/examples/ArmSimulation/include/subsystems/Arm.h

@@ -53,6 +53,7 @@ class Arm {
       kMinAngle,
       kMaxAngle,
       true,
+      0_deg,
       {kArmEncoderDistPerPulse}};
   frc::sim::EncoderSim m_encoderSim{m_encoder};