This introduces the ability to allocate Vulkan images which can be
shared across graphics APIs or across processes using the Linux dma-buf
interface.
The create_shareable_vulkan_image function takes a VulkanContext, image
width, height, and format, and an array of DRM format modifiers
representing image memory layouts accepted by the caller. The function
will intersect this list with the list of modifiers supported by the
Vulkan implementation, ensuring the resulting image uses one of those
layouts (exactly which one is up to the implementation). The function
will return a VulkanImage object, which is reference-counted and
encapsulates the VkImage itself as well as the backing memory
allocation. It also stores various image parameters such as usage,
tiling, etc.
The VulkanImage::get_dma_buf_fd function will create a file descriptor
representing the image's backing dma-buf which can then be imported by a
different API or sent over a unix domain socket.
Coverity static analysis reports that the code that scans the queue
families for one that has the graphics bit, can be -1 if none are
found, which could cause a problem when the -1 (signed) value is
used later as an index in a uint32_t (unsigned) variable.
Its not immediately clear how often this could occur, not finding
a queue family with the graphics bit, but adding some protecting
just in case.
