[wpilib] Counter: Fix default distance per pulse, add distance and rate to C++ (#5796)

- Default distance per pulse in java was 0; 1 is a more reasonable default
- C++ was missing this functionality

wpilibc/src/main/native/include/frc/Counter.h

@@ -343,6 +343,34 @@ class Counter : public CounterBase,
 
   int GetFPGAIndex() const;
 
+  /**
+   * Set the distance per pulse for this counter. This sets the multiplier used
+   * to determine the distance driven based on the count value from the encoder.
+   * Set this value based on the Pulses per Revolution and factor in any gearing
+   * reductions. This distance can be in any units you like, linear or angular.
+   *
+   * @param distancePerPulse The scale factor that will be used to convert
+   * pulses to useful units.
+   */
+  void SetDistancePerPulse(double distancePerPulse);
+
+  /**
+   * Read the current scaled counter value. Read the value at this instant,
+   * scaled by the distance per pulse (defaults to 1).
+   *
+   * @return The distance since the last reset
+   */
+  double GetDistance() const;
+
+  /**
+   * Get the current rate of the Counter. Read the current rate of the counter
+   * accounting for the distance per pulse value. The default value for distance
+   * per pulse (1) yields units of pulses per second.
+   *
+   * @return The rate in units/sec
+   */
+  double GetRate() const;
+
   // CounterBase interface
   /**
    * Read the current counter value.
@@ -434,6 +462,7 @@ class Counter : public CounterBase,
 
  private:
   int m_index = 0;  // The index of this counter.
+  double m_distancePerPulse = 1;
 
   friend class DigitalGlitchFilter;
 };