vulkan/wsi: prefer the Wayland linux-dmabuf protocol

vulkan/wsi: prefer the Wayland linux-dmabuf protocol

When the linux-dmabuf protocol is available, prefer it over the old
wl_drm protocol. Previously wl_drm was used when modifiers aren't
supported, however linux-dmabuf supports formats without modifiers too.
In this case, linux-dmabuf will send a DRM_FORMAT_MOD_INVALID modifier
for each supported format [1].

All of this allows compositors to better handle these buffers, getting a
DMA-BUF and implementing features like direct scan-out.

A similar logic has been implemented for EGL [2].

In this patch, we bind to linux-dmabuf even if the driver doesn't support
modifiers. In this case the formats advertised by the compositor will
still be added to the display->dmabuf.formats list.

In wsi_wl_image_init, drop the assertions that display->drm_wrapper and
display->dmabuf.wl_dmabuf can't be both present. If the driver doesn't
support modifiers, the modifier is already set to DRM_FORMAT_MOD_INVALID.
If the parent compositor doesn't support modifiers, the modifiers list
passed to wsi_create_native_image will be empty, and the common code
will ensure that the image's modifier is set to DRM_FORMAT_MOD_INVALID.

In wsi_wl_surface_create_swapchain, create the wl_proxy proxy if we've
bound to it earlier. Don't decide to create the proxy depending on the
number of supported modifiers.

[1]: https://gitlab.freedesktop.org/wayland/wayland-protocols/commit/fb9b2a87317c77e26283da5f6c9559d709f6fdcd
[2]: https://gitlab.freedesktop.org/mesa/mesa/-/commit/c376865f5eeca535c4aa8e33bcf166052c1ce2f2

Signed-off-by: Simon Ser <contact@emersion.fr>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4942>