[hal,wpilib] Rename "Test" robot mode to "Utility" (#8782)

The "Utility" name better matches its intended generic use case and
avoids overloaded terminology with unit testing (e.g. the need to name
the opmode annotation `@TestOpMode`).

The driver station will also be updated to reflect this change.

developerRobot/src/main/java/wpilib/robot/Robot.java

@@ -29,9 +29,9 @@ public class Robot extends TimedRobot {
   @Override
   public void teleopPeriodic() {}
 
-  /** This function is called periodically during test mode. */
+  /** This function is called periodically during utility mode. */
   @Override
-  public void testPeriodic() {}
+  public void utilityPeriodic() {}
 
   /** This function is called periodically during all modes. */
   @Override

developerRobot/src/main/native/cpp/Robot.cpp

@@ -35,7 +35,7 @@ class Robot : public wpi::TimedRobot {
   /**
    * This function is called periodically during test mode
    */
-  void TestPeriodic() override {}
+  void UtilityPeriodic() override {}
 
   /**
    * This function is called periodically during all modes