[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;

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

@@ -8,6 +8,8 @@
 #include <memory>
 #include <utility>
 
+#include <wpi/deprecated.h>
+
 #include "frc2/command/Command.h"
 #include "frc2/command/CommandPtr.h"
 
@@ -34,6 +36,7 @@ class CommandHelper : public Base {
   }
 
  protected:
+  WPI_DEPRECATED("Use ToPtr() instead")
   std::unique_ptr<Command> TransferOwnership() && override {
     return std::make_unique<CRTP>(std::move(*static_cast<CRTP*>(this)));
   }

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

@@ -17,6 +17,7 @@
 #include <utility>
 #include <vector>
 
+#include <wpi/deprecated.h>
 #include <wpi/sendable/SendableBuilder.h>
 
 #include "frc2/command/Command.h"
@@ -134,6 +135,7 @@ class SelectCommand : public CommandHelper<Command, SelectCommand<Key>> {
   }
 
  protected:
+  WPI_DEPRECATED("Use ToPtr() instead")
   std::unique_ptr<Command> TransferOwnership() && override {
     return std::make_unique<SelectCommand>(std::move(*this));
   }