Draft: Add Squeekboard-data package containing keyboard yaml

This is needed for squeek2lvgl to work without downloading the keyboard definitions at runtime. Squeek2lvgl is a dependency of Unl0kr, which is minimal replacement for osk-sdl. The upstream osk-sdl devs are pushing its replacement, so this package will eventually be necessary for encryption.

More than happy to adjust the method here, but as there doesn't seem to be a way to build-depend on source packages and we can't pull the files over the internet on the buildd network this seems like the best option.