[wpilib] Add isTestEnabled and minor docs cleanup (#5172)

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

@@ -209,6 +209,14 @@ class DriverStation final {
    */
   static bool IsTest();
 
+  /**
+   * Check if the DS is commanding Test mode and if it has enabled the robot.
+   *
+   * @return True if the robot is being commanded to be in Test mode and
+   * enabled.
+   */
+  static bool IsTestEnabled();
+
   /**
    * Check if the DS is attached.
    *