Vulkan/wsi: Implement VK_EXT_display_surface_counter

Vulkan/wsi: Implement VK_EXT_display_surface_counter

This extension is required to support EXT_display_control as it offers a
way to query whether the vblank counter is supported.  Internally, it is
implemented using a fake MESA extension which provides a chain-in to
GetSurfaceCapabilities2KHR which contains the one added field.  This has
the advantage of reducing number of callbacks needed in the back-ends.
It also means that anything chained into GetSurfaceCapabilities2EXT
through VkSurfaceCapabilities2KHR::pNext so we only need to handle
crawling the pNext chain once per back-end.

Reviewed-by: Keith Packard <keithp@keithp.com>