Add more doc fixes for Vulkan types

Add dummy typedefs just for qdoc, this way the types show up in
the generated docs.

Change-Id: I408eeb5c4c1cbbb8cd7df8ca3c9c6b7c64b0ca88
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

src/gui/vulkan/qvulkaninstance.h

@@ -62,6 +62,9 @@ typedef void* VkInstance;
 typedef void* VkPhysicalDevice;
 typedef void* VkDevice;
 typedef int VkResult;
+typedef int VkImageLayout;
+typedef int VkDebugReportFlagsEXT;
+typedef int VkDebugReportObjectTypeEXT;
 #endif
 
 #include <QtCore/qbytearraylist.h>