backend/wayland: use wlr_swapchain

Depends on #2496

TODO:

• Use wlr_swapchain for main surface
• Use wlr_swapchain for cursor surface
• Intersect linux-dmabuf-v1 formats with render formats

Future work:

• Don't create a wl_buffer on each commit -- cache them (https://github.com/swaywm/wlroots/pull/2538)
• Use linux-dmabuf hints to get render FD

References: #1352 (closed)