Fix two major synchronization issues in `wgpu_val::vulkan`:
- Properly order queue command buffer submissions. Due to Mesa bugs, two semaphores are required even though the Vulkan spec says that only one should be necessary.
- Properly manage surface texture acquisition and presentation:
- Acquiring a surface texture can return while the presentation engine is still displaying the texture. Applications must wait for a semaphore to be signaled before using the acquired texture.
- Presenting a surface texture requires a semaphore to ensure that drawing is complete before presentation occurs.
Co-authored-by: Jim Blandy <jimb@red-bean.com>
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