This doesn't make any difference now, but will allow us to copy
subregions more easily. This is not obvious, but here's a quick
explanation:
Leaving 'bufferRowLength' and 'bufferImageHeight' implies that
Vulkan will assume the size passed in the 'imageExtent' field.
Right now, this assumption is correct - the only user of this
function is the glyph cache, and it only copies and uploads
exact rects. Next commits will change that assumption, so we
must pass 'buffer*' fields, and tell Vulkan, "this part of the
buffer represents an image of width x height, and I want the
subregion (x, y, smallerWidth, smallerHeight) of this image".
When creating an image using gsk_vulkan_image_new_for_framebuffer(),
it passes VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL.
However, this is a mistake. The spec demands that the initial
layout must be either VK_IMAGE_LAYOUT_UNDEFINED or
VK_IMAGE_LAYOUT_PREINITIALIZED.
Apparently this was an oversight from commit b97fb75146, since the
commit message even documents that, and all other calls pass either
VK_IMAGE_LAYOUT_UNDEFINED or VK_IMAGE_LAYOUT_PREINITIALIZED.
Create framebuffer images using VK_IMAGE_LAYOUT_UNDEFINED, which is
what was originally expected.
Multiple images in the before barrier array are defined with
VK_ACCESS_TRANSFER_WRITE_BIT and VK_ACCESS_TRANSFER_READ_BIT,
which requires passing VK_PIPELINE_STAGE_TRANSFER_BIT and
VK_PIPELINE_STAGE_HOST_BIT to vkCmdPipelineBarrier().
Pass these flags correctly.
