Refactor L0 command-buffer cleanup.

Coverity has reported that there is the possibility of the
command-buffer destructor throwing an exception from its calls
to `CleanupCompletedEvent`.

This is from an underlying `throw` in
[GetQueue](https://github.com/oneapi-src/unified-runtime/blob/main/source/adapters/level_zero/queue.hpp#L890)
when a `dynamic_cast` doesn't behave as expected. I initially tried
changing this to an assert but the V2 Level Zero adapter is triggering
this case while in it's developmental state, so an assert brings down the
whole test suite rather than just being reported as a fail (the UR
loader catches exceptions and returns them as error codes).

Therefore this PR addresses the issue by moving the calls to
`CleanupCompletedEvent()` outside of the command-buffer destructor. This allows
us us to report an error from command-buffer release by doing cleanup prior to
calling the destructor, without the risk of throwing an exception.

Author: EwanC

source/adapters/level_zero/command_buffer.cpp

@@ -424,9 +424,7 @@ ur_exp_command_buffer_handle_t_::ur_exp_command_buffer_handle_t_(
   urDeviceRetain(Device);
 }
 
-// The ur_exp_command_buffer_handle_t_ destructor releases all the memory
-// objects allocated for command_buffer management.
-ur_exp_command_buffer_handle_t_::~ur_exp_command_buffer_handle_t_() {
+void ur_exp_command_buffer_handle_t_::cleanupCommandBufferResources() {
   // Release the memory allocated to the Context stored in the command_buffer
   urContextRelease(Context);
 
@@ -703,6 +701,7 @@ urCommandBufferReleaseExp(ur_exp_command_buffer_handle_t CommandBuffer) {
   if (!CommandBuffer->RefCount.decrementAndTest())
     return UR_RESULT_SUCCESS;
 
+  CommandBuffer->cleanupCommandBufferResources();
   delete CommandBuffer;
   return UR_RESULT_SUCCESS;
 }

source/adapters/level_zero/command_buffer.hpp

@@ -34,8 +34,6 @@ struct ur_exp_command_buffer_handle_t_ : public _ur_object {
       ur_event_handle_t WaitEvent, ur_event_handle_t AllResetEvent,
       const ur_exp_command_buffer_desc_t *Desc, const bool IsInOrderCmdList);
 
-  ~ur_exp_command_buffer_handle_t_();
-
   void registerSyncPoint(ur_exp_command_buffer_sync_point_t SyncPoint,
                          ur_event_handle_t Event);
 
@@ -65,6 +63,10 @@ struct ur_exp_command_buffer_handle_t_ : public _ur_object {
    */
   ze_command_list_handle_t chooseCommandList(bool PreferCopyEngine);
 
+  // Releases the resources associated with the command-buffer before the
+  // command-buffer object is destroyed.
+  void cleanupCommandBufferResources();
+
   // UR context associated with this command-buffer
   ur_context_handle_t Context;
   // Device associated with this command buffer