Fix Vulkan validation errors for simultaneous command buffer submission.
Currently, swapchain acquire/release command submissions trigger validations warning VUID-vkQueueSubmit-pCommandBuffers-00071 (If any element of the pCommandBuffers member of any element of pSubmits was not recorded with the VK_COMMAND_BUFFER_USAGE_SIMULTANEOUS_USE_BIT, it must not be in the pending state).
This is fixed by submitting acquire/release with a fence and waiting on the fence prior to the next submission of that same command buffer (per-image).