[hal] Add HAL_Shutdown and simulation shutdown callbacks

This is useful for clean shutdown of simulation extensions.

wpilibc/src/main/native/include/frc/RobotBase.h

@@ -10,6 +10,7 @@
 #include <chrono>
 #include <thread>
 
+#include <hal/HALBase.h>
 #include <hal/Main.h>
 #include <wpi/condition_variable.h>
 #include <wpi/mutex.h>
@@ -89,6 +90,8 @@ int StartRobot() {
     impl::RunRobot<Robot>(m, &robot);
   }
 
+  HAL_Shutdown();
+
   return 0;
 }