[commands] Deprecate C++ TransferOwnership() (#6095)

It has been completely replaced with ToPtr().

wpilibNewCommands/src/main/native/include/frc2/command/Command.h

@@ -432,6 +432,7 @@ class Command : public wpi::Sendable, public wpi::SendableHelper<Command> {
    * Transfers ownership of this command to a unique pointer.  Used for
    * decorator methods.
    */
+  [[deprecated("Use ToPtr() instead")]]
   virtual std::unique_ptr<Command> TransferOwnership() && = 0;
 
   std::optional<std::string> m_previousComposition;