vulkan: Add a core vk_sampler struct

vulkan: Add a core vk_sampler struct

Unlike some other core structs, I didn't bother to copy the entire
VkSamplerCreateInfo into the sampler.  There isn't typcially a lot of
pre-processing we can or need to do here and we may as well keep the
struct small for now.  It does, however, handle most things involving
chain-in structs.

Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24335>