Vulkan: Clean up VAO cached resources. We can actually store a pointer to the base ResourceVk instead of BufferVk for updating serials. This will work a little nicer with streaming vertex data, which won't have a BufferVk but will have an accessible ResourceVk pointer. Also add an element array resource pointer for serial update. This was missing and could lead to incorrect behaviour. Also change the types of the caches from std::vector to gl::AttribArray, which is a std::array. Bug: angleproject:2264 Change-Id: Ibd79b7676b5dbc3875ae9d110be477d228e01c5c Reviewed-on: https://chromium-review.googlesource.com/798170 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org>