message: VulkanDevice: Request indenpendentBlend.
  This is a core NXT feature but wasn't enabled, causing the Vulkan
  validation layers to produce an error.
diff: @@ -471,6 +471,9 @@ namespace backend { namespace vulkan {
  usedKnobs->swapchain = true;
  }
  + // Always require independentBlend because it is a core NXT feature,
  + usedKnobs->features.independentBlend = VK_TRUE;
  +
  // Find a universal queue family
  {
  constexpr uint32_t kUniversalFlags =
  