vkimagebufferpool: allow specifying initial image layout
The Vulkan image buffer pool currently defaults to performing a layout transition to VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL
, with some special exceptions for video usages. This may not be a legal transition depending on the usage, and in general I don't really think it makes sense to be trying to divine a layout from the usage anyway. Provide an API to explicitly control the initial image layout.
cc @vjaquez