This will be needed for dmabuf-hints support (wayland-protocols!8 (merged)) for telling the client which device we're using for compositing, without relying on wl_drm. Using EGL devices mean that this will work across all backends.
Right now, it doesn't do a whole lot except print some new log messages, but this lot of work still makes sense without the rest of dmabuf-hints being implemented.
This also includes some refactoring of EGL display creation and EGL client extension handling, to provide a better place to put using the EGL device extensions.
See also: https://www.khronos.org/registry/EGL/extensions/EXT/EGL_EXT_device_query.txt https://www.khronos.org/registry/EGL/extensions/EXT/EGL_EXT_device_drm.txt