Fix the depth buffer clearing on Vulkan
Fix the depth buffer clearing on Vulkan

This isn't quite perfect, but I suspect the remaining problems are actually to do
with alpha blending.  Apparently I hadn't removed the clear on the renderpass begin.
And the explicit clear was, ahem, complete nonsense.

Alwo: Use a separate depth buffer per swapchain image.  I have read that this is not
required, but it makes things cleaner.

StrayLightning/aeolius,StrayLightning/aeolius,StrayLightning/aeolius