turnip: Implement vkCreateQueryPool for occlusion queries

turnip: Implement vkCreateQueryPool for occlusion queries

General structure is inspired by anv's implementation in genX_query.c.
We define a packed struct that tracks sample count at the beginning of
the query and at the end; the result of the occlusion query is then
slot->end - slot->begin.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3279>