[wpilib] Document simulation APIs (#3079)

- Remove sim checkstyle suppression
- Add [[nodiscard]] to C++ register callback functions
- Add a couple of missing sim functions

Co-authored-by: Peter Johnson <johnson.peter@gmail.com>
Co-authored-by: Starlight220 <yotamshlomi@gmail.com>

wpilibc/src/main/native/include/frc/simulation/RelaySim.h

@@ -33,34 +33,107 @@ class RelaySim {
    */
   explicit RelaySim(int channel);
 
-  std::unique_ptr<CallbackStore> RegisterInitializedForwardCallback(
-      NotifyCallback callback, bool initialNotify);
+  /**
+   * Register a callback to be run when the forward direction is initialized.
+   *
+   * @param callback the callback
+   * @param initialNotify whether to run the callback with the initial state
+   * @return the CallbackStore object associated with this callback
+   */
+  [[nodiscard]] std::unique_ptr<CallbackStore>
+  RegisterInitializedForwardCallback(NotifyCallback callback,
+                                     bool initialNotify);
 
+  /**
+   * Check whether the forward direction has been initialized.
+   *
+   * @return true if initialized
+   */
   bool GetInitializedForward() const;
 
+  /**
+   * Define whether the forward direction has been initialized.
+   *
+   * @param initializedForward whether this object is initialized
+   */
   void SetInitializedForward(bool initializedForward);
 
-  std::unique_ptr<CallbackStore> RegisterInitializedReverseCallback(
-      NotifyCallback callback, bool initialNotify);
+  /**
+   * Register a callback to be run when the reverse direction is initialized.
+   *
+   * @param callback the callback
+   * @param initialNotify whether to run the callback with the initial state
+   * @return the CallbackStore object associated with this callback
+   */
+  [[nodiscard]] std::unique_ptr<CallbackStore>
+  RegisterInitializedReverseCallback(NotifyCallback callback,
+                                     bool initialNotify);
 
+  /**
+   * Check whether the reverse direction has been initialized.
+   *
+   * @return true if initialized
+   */
   bool GetInitializedReverse() const;
 
+  /**
+   * Define whether the reverse direction has been initialized.
+   *
+   * @param initializedReverse whether this object is initialized
+   */
   void SetInitializedReverse(bool initializedReverse);
 
-  std::unique_ptr<CallbackStore> RegisterForwardCallback(
+  /**
+   * Register a callback to be run when the forward direction changes state.
+   *
+   * @param callback the callback
+   * @param initialNotify whether to run the callback with the initial state
+   * @return the CallbackStore object associated with this callback
+   */
+  [[nodiscard]] std::unique_ptr<CallbackStore> RegisterForwardCallback(
       NotifyCallback callback, bool initialNotify);
 
+  /**
+   * Check whether the forward direction is active.
+   *
+   * @return true if active
+   */
   bool GetForward() const;
 
+  /**
+   * Set whether the forward direction is active.
+   *
+   * @param forward true to make active
+   */
   void SetForward(bool forward);
 
-  std::unique_ptr<CallbackStore> RegisterReverseCallback(
+  /**
+   * Register a callback to be run when the reverse direction changes state.
+   *
+   * @param callback the callback
+   * @param initialNotify whether to run the callback with the initial state
+   * @return the CallbackStore object associated with this callback
+   */
+  [[nodiscard]] std::unique_ptr<CallbackStore> RegisterReverseCallback(
       NotifyCallback callback, bool initialNotify);
 
+  /**
+   * Check whether the reverse direction is active.
+   *
+   * @return true if active
+   */
   bool GetReverse() const;
 
+  /**
+   * Set whether the reverse direction is active.
+   *
+   * @param reverse true to make active
+   */
   void SetReverse(bool reverse);
 
+  /**
+   * Reset all simulation data.
+   */
   void ResetData();
 
  private: