zink: reject more illegal blits
Vulkan has some additional restrictions for vkCmdBlitImage that we weren't testing for. Quting the Vulkan 1.2 spec, section 20.5 "Image Copies with Scaling", "Valid Usage" subsection:
- If either of srcImage or dstImage was created with a signed integer VkFormat, the other must also have been created with a signed integer VkFormat
- If either of srcImage or dstImage was created with an unsigned integer VkFormat, the other must also have been created with an unsigned integer VkFormat.
So let's make sure we reject these illegal blits.