[wpilib] ExHub Follower Fixes (#8892)

A chunk of updates to followers on Expansion Hub

Fixes followers not implicitly enabling.
Allows followers to follow other followers
Throws exceptions on construction if a follower cycle is detected.
Allows reversing followers.

The enable thing will fix
https://github.com/wpilibsuite/SystemcoreTesting/discussions/259#discussioncomment-16886195

Closes #8843

Depends on https://github.com/wpilibsuite/scservices/pull/30

wpilibc/src/main/native/include/wpi/hardware/expansionhub/ExpansionHub.hpp

@@ -79,6 +79,9 @@ class ExpansionHub {
   bool CheckAndReserveMotor(int channel);
   void UnreserveMotor(int channel);
 
+  void AddFollower(int leaderChannel, int followerChannel);
+  void RemoveFollower(int followerChannel);
+
   void ReportUsage(std::string_view device, std::string_view data);
 
   class DataStore;

wpilibc/src/main/native/include/wpi/hardware/expansionhub/ExpansionHubMotor.hpp

@@ -19,6 +19,14 @@ namespace wpi {
  * ExpansionHub. */
 class ExpansionHubMotor {
  public:
+  /** The direction to follow a leader motor in when using the follow method. */
+  enum class FollowDirection {
+    /** Follow the leader motor in the same direction. */
+    Aligned,
+    /** Follow the leader motor in the opposite direction. */
+    Opposed
+  };
+
   /**
    * Constructs a servo at the requested channel on a specific USB port.
    *
@@ -144,8 +152,14 @@ class ExpansionHubMotor {
    * Additionally, the direction of both motors will be the same.
    *
    * @param leader The motor to follow
+   * @param direction The direction to follow the leader
    */
-  void Follow(const ExpansionHubMotor& leader);
+  void Follow(const ExpansionHubMotor& leader, FollowDirection direction);
+
+  /**
+   * Stops following the currently set leader motor.
+   */
+  void Unfollow();
 
  private:
   ExpansionHub m_hub;