[L0] Make destructor of the context virtual

to make sure that v2::context will release all the resources
on context destruction.

source/adapters/level_zero/context.hpp

@@ -43,6 +43,8 @@ struct ur_context_handle_t_ : _ur_object {
 
  ur_context_handle_t_(ze_context_handle_t ZeContext) : ZeContext{ZeContext} {}
 
+ virtual ~ur_context_handle_t_() {}
+
  // A L0 context handle is primarily used during creation and management of
  // resources that may be used by multiple devices.
  // This field is only set at ur_context_handle_t creation time, and cannot