In the previous change, I added the uuid files. In this change, we
check the libavutil version and if it's too old, we compile in our
local copy.
We have to change the include paths of the uuid code to find some other
libavutil headers, but nothing beyond that.
To avoid taking a dependency on ffmpeg 5.1 before we're ready (we need
a newer Ubuntu LTS release to drop ffmpeg 4.x support), ut not force us
to wait to add support for picking Vulkan devices by UUID, I'm copying
the uuid code from ffmpeg into mpv. It's one file with no private
dependencies, so it's easier to copy than to reimplement in any other
way.
Licence is LGPL so matches us.
