[wpilib] Add Timer.isRunning() method (#7220)

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

@@ -111,6 +111,13 @@ class Timer {
    */
   bool AdvanceIfElapsed(units::second_t period);
 
+  /**
+   * Whether the timer is currently running.
+   *
+   * @return true if running.
+   */
+  bool IsRunning() const;
+
   /**
    * Return the FPGA system clock time in seconds.
    *