[async] Update includes of async headers to new path (#4760)

content_handler/vulkan_surface.cc

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include <async/default.h>
+#include <lib/async/default.h>
 
 #include "flutter/content_handler/vulkan_surface.h"
 #include "flutter/common/threads.h"

content_handler/vulkan_surface.h

@@ -4,7 +4,7 @@
 
 #pragma once
 
-#include <async/cpp/wait.h>
+#include <lib/async/cpp/wait.h>
 #include <zx/event.h>
 #include <zx/vmo.h>