vulkan: Upload cairo images "directly"

vulkan: Upload cairo images "directly"

Instead of using the upload vfunc and going via the code in
GskVulkanImage, copy/paste the relevant code into the command() vfunc.

This is meant to achieve multiple things:
1. Get rid of GskVulkanUploader and its own command buffer and general
   non-integration with operations.
2. Get rid of GskVulkanOp:upload()
3. Get the upload/download code machinery for GskVulkanImage and put it
   with the actual operations.

The current code can't do direct upload/download, that will follow in a
future commit.