task list for vulkan renderer

This is a list of orthogonal changes in !412 (merged), to give an idea of what needs to be done and what to expect next for myself and for reviewers

• fix virgl_renderer_resource_get_map_info for untyped blob resources (!458 (merged))
• fix vrend_decode_ctx_attach_resource for untyped blob resources (!465 (merged))
• add virgl_renderer_context_create_with_flags (!432 (merged))
• add per-context fencing (!471 (merged))
• add vulkan renderer (!412 (merged))
• move https://gitlab.freedesktop.org/olv/venus-protocol under virgl
• add vtest changes to use virgl_renderer_context_create_with_flags (!432 (merged))
• add vtest changes to use virgl_renderer_resource_create_blob (!412 (merged))
• add vtest changes for per-context fencing (!412 (merged))
• add vtest changes to support Vulkan contexts (!412 (merged))

Note that all public API changes should be guarded by VIRGL_RENDERER_UNSTABLE_APIS until the corresponding kernel and virtio-gpu changes are finalized.