[wpilib] Fix HolonomicDriveController atReference() behavior (#3163)

The atReference() method previously used the rotation error between the
desired trajectory state and the current pose. This was a bug because we
allow teams to use custom rotation setpoints and that wasn't being taken
into account.

wpilibc/src/main/native/include/frc/controller/HolonomicDriveController.h

@@ -98,6 +98,7 @@ class HolonomicDriveController {
 
  private:
   Pose2d m_poseError;
+  Rotation2d m_rotationError;
   Pose2d m_poseTolerance;
   bool m_enabled = true;