[0.4] Fix depth attachment transitions

[kvark]

[2020-01-15T18:03:41Z ERROR gfx_backend_vulkan] 
VALIDATION [VUID-VkImageSubresource-aspectMask-parameter (0)] : vkCmdPipelineBarrier(): Depth-only image formats must have the VK_IMAGE_ASPECT_DEPTH_BIT set. The Vulkan spec states: aspectMask must be a valid combination of VkImageAspectFlagBits values (https://www.khronos.org/registry/vulkan/specs/1.1-extensions/html/vkspec.html#VUID-VkImageSubresource-aspectMask-parameter)
object info: (type: IMAGE, hndl: 60)

[2020-01-15T18:03:41Z ERROR gfx_backend_vulkan] 
VALIDATION [UNASSIGNED-CoreValidation-DrawState-InvalidImageLayout (0)] : Submitted command buffer expects VkImage 0x3c[]  (subresource: aspectMask 0x2 array layer 0, mip level 0) to be in layout VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL--instead, current layout is VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL.
object info: (type: COMMAND_BUFFER, hndl: 94914754889856)

[2020-01-15T18:03:42Z ERROR gfx_backend_vulkan] 
VALIDATION [UNASSIGNED-CoreValidation-DrawState-InvalidImageLayout (0)] : Submitted command buffer expects VkImage 0x3c[]  (subresource: aspectMask 0x2 array layer 0, mip level 0) to be in layout VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL--instead, current layout is VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL.
object info: (type: COMMAND_BUFFER, hndl: 94914754886576)

This is very likely not a problem in master, but we need to make a patch for the released version.

[kvark]

I think it's actually a consequence of #458 bug. Once the STORAGE usage is correctly identified, I'm no longer seeing these errors.