[wpimath] improve LTVUnicycleController docs (NFC)

Document the states and inputs so it isn't necessary to look at the code
Fix max velocity throws doc

wpimath/src/main/java/edu/wpi/first/math/controller/LTVUnicycleController.java

@@ -54,8 +54,9 @@ private enum State {
 
   /**
    * Constructs a linear time-varying unicycle controller with default maximum desired error
-   * tolerances of (0.0625 m, 0.125 m, 2 rad) and default maximum desired control effort of (1 m/s,
-   * 2 rad/s).
+   * tolerances of (x = 0.0625 m, y = 0.125 m, heading = 2 rad), default maximum desired control
+   * effort of (linear velocity = 1 m/s, angular velocity = 2 rad/s), and default maximum Velocity
+   * of 9 m/s.
    *
    * @param dt Discretization timestep in seconds.
    */
@@ -65,13 +66,13 @@ public LTVUnicycleController(double dt) {
 
   /**
    * Constructs a linear time-varying unicycle controller with default maximum desired error
-   * tolerances of (0.0625 m, 0.125 m, 2 rad) and default maximum desired control effort of (1 m/s,
-   * 2 rad/s).
+   * tolerances of (x = 0.0625 m, y = 0.125 m, heading = 2 rad), default maximum desired control
+   * effort of (1 m/s, 2 rad/s).
    *
    * @param dt Discretization timestep in seconds.
    * @param maxVelocity The maximum velocity in meters per second for the controller gain lookup
    *     table. The default is 9 m/s.
-   * @throws IllegalArgumentException if maxVelocity <= 0.
+   * @throws IllegalArgumentException if maxVelocity <= 0 m/s or >= 15 m/s.
    */
   public LTVUnicycleController(double dt, double maxVelocity) {
     this(VecBuilder.fill(0.0625, 0.125, 2.0), VecBuilder.fill(1.0, 2.0), dt, maxVelocity);
@@ -84,8 +85,11 @@ public LTVUnicycleController(double dt, double maxVelocity) {
    * href="https://docs.wpilib.org/en/stable/docs/software/advanced-controls/state-space/state-space-intro.html#lqr-tuning">https://docs.wpilib.org/en/stable/docs/software/advanced-controls/state-space/state-space-intro.html#lqr-tuning</a>
    * for how to select the tolerances.
    *
-   * @param qelems The maximum desired error tolerance for each state.
-   * @param relems The maximum desired control effort for each input.
+   * <p>The default maximum Velocity is 9 m/s.
+   *
+   * @param qelems The maximum desired error tolerance for each state (x, y, heading).
+   * @param relems The maximum desired control effort for each input (linear velocity, angular
+   *     velocity).
    * @param dt Discretization timestep in seconds.
    */
   public LTVUnicycleController(Vector<N3> qelems, Vector<N2> relems, double dt) {
@@ -99,8 +103,9 @@ public LTVUnicycleController(Vector<N3> qelems, Vector<N2> relems, double dt) {
    * href="https://docs.wpilib.org/en/stable/docs/software/advanced-controls/state-space/state-space-intro.html#lqr-tuning">https://docs.wpilib.org/en/stable/docs/software/advanced-controls/state-space/state-space-intro.html#lqr-tuning</a>
    * for how to select the tolerances.
    *
-   * @param qelems The maximum desired error tolerance for each state.
-   * @param relems The maximum desired control effort for each input.
+   * @param qelems The maximum desired error tolerance for each state (x, y, heading).
+   * @param relems The maximum desired control effort for each input (linear velocity, angular
+   *     velocity).
    * @param dt Discretization timestep in seconds.
    * @param maxVelocity The maximum velocity in meters per second for the controller gain lookup
    *     table. The default is 9 m/s.

wpimath/src/main/native/include/frc/controller/LTVUnicycleController.h

@@ -33,13 +33,14 @@ class WPILIB_DLLEXPORT LTVUnicycleController {
  public:
   /**
    * Constructs a linear time-varying unicycle controller with default maximum
-   * desired error tolerances of (0.0625 m, 0.125 m, 2 rad) and default maximum
-   * desired control effort of (1 m/s, 2 rad/s).
+   * desired error tolerances of (x = 0.0625 m, y = 0.125 m, heading = 2 rad)
+   * and default maximum desired control effort of (linear velocity = 1 m/s,
+   * angular velocity = 2 rad/s).
    *
    * @param dt Discretization timestep.
    * @param maxVelocity The maximum velocity for the controller gain lookup
    *                    table.
-   * @throws std::domain_error if maxVelocity <= 0.
+   * @throws std::domain_error if maxVelocity <= 0 m/s or >= 15 m/s.
    */
   explicit LTVUnicycleController(
       units::second_t dt, units::meters_per_second_t maxVelocity = 9_mps);
@@ -51,8 +52,10 @@ class WPILIB_DLLEXPORT LTVUnicycleController {
    * https://docs.wpilib.org/en/stable/docs/software/advanced-controls/state-space/state-space-intro.html#lqr-tuning
    * for how to select the tolerances.
    *
-   * @param Qelems The maximum desired error tolerance for each state.
-   * @param Relems The maximum desired control effort for each input.
+   * @param Qelems The maximum desired error tolerance for each state (x, y,
+   *               heading).
+   * @param Relems The maximum desired control effort for each input (linear
+   *               velocity, angular velocity).
    * @param dt     Discretization timestep.
    * @param maxVelocity The maximum velocity for the controller gain lookup
    *                    table.