zink: fix vertex-stride wrangling
Because Gallium and Vulkan disagree on what kind of state strides is, we need to wrangle this state a bit, and up until now, we've been simply fixing this up while binding the vertex-buffers.
But this isn't robust, because the vertex element state might be bound after the vertex-buffer state was bound. We also need to take binding-map into account, which we're currently missing as well.
Instead, w need to deal with this at a place where we know what's being used for both of these. So let's do this during draw instead.
Ideally, we'd also do some dirty-tracking to know if this is needed or not, but I believe Mike has some patches in this areas lined up, so it might be easier to wait for those.