[examples] Make DriveDistanceOffboard example work in sim (#3199)

Adds some basic functionality to the ExampleMotorController so that
controller inputs show up in LiveWindow widgets in simulation.

wpilibcExamples/src/main/cpp/examples/DriveDistanceOffboard/include/ExampleSmartMotorController.h

@@ -68,9 +68,9 @@ class ExampleSmartMotorController : public frc::SpeedController {
    */
   void ResetEncoder() {}
 
-  void Set(double speed) override {}
+  void Set(double speed) override { m_value = speed; }
 
-  double Get() const override { return 0; }
+  double Get() const override { return m_value; }
 
   void SetInverted(bool isInverted) override {}
 
@@ -81,4 +81,7 @@ class ExampleSmartMotorController : public frc::SpeedController {
   void StopMotor() override {}
 
   void PIDWrite(double output) override {}
+
+ private:
+  double m_value = 0.0;
 };

wpilibjExamples/src/main/java/edu/wpi/first/wpilibj/examples/drivedistanceoffboard/ExampleSmartMotorController.java

@@ -18,6 +18,8 @@ public class ExampleSmartMotorController implements SpeedController {
     kMovementWitchcraft
   }
 
+  double m_value;
+
   /**
    * Creates a new ExampleSmartMotorController.
    *
@@ -73,11 +75,13 @@ public class ExampleSmartMotorController implements SpeedController {
   public void resetEncoder() {}
 
   @Override
-  public void set(double speed) {}
+  public void set(double speed) {
+    m_value = speed;
+  }
 
   @Override
   public double get() {
-    return 0;
+    return m_value;
   }
 
   @Override