[examples] Update C++ examples to use CommandPtr (#5988)

Co-authored-by: Tyler Veness <calcmogul@gmail.com>

wpilibcExamples/src/main/cpp/examples/MecanumControllerCommand/include/Robot.h

@@ -4,6 +4,8 @@
 
 #pragma once
 
+#include <optional>
+
 #include <frc/TimedRobot.h>
 #include <frc2/command/Command.h>
 
@@ -24,7 +26,7 @@ class Robot : public frc::TimedRobot {
  private:
   // Have it null by default so that if testing teleop it
   // doesn't have undefined behavior and potentially crash.
-  frc2::Command* m_autonomousCommand = nullptr;
+  std::optional<frc2::CommandPtr> m_autonomousCommand;
 
   RobotContainer m_container;
 };