[examples] Update Field2d position in periodic() (#2928)

This ensures that the robot position will be updated in dashboards like Glass when running on real hardware.

wpilibcExamples/src/main/cpp/examples/SimpleDifferentialDriveSimulation/include/Drivetrain.h

@@ -64,6 +64,7 @@ class Drivetrain {
   frc::Pose2d GetPose() const { return m_odometry.GetPose(); }
 
   void SimulationPeriodic();
+  void Periodic();
 
  private:
   static constexpr units::meter_t kTrackWidth = 0.381_m * 2;