`mpv.vapoursynth.python3.sitePackages` expands to `/lib/python3.8/site-packages`, thus `/lib/lib/python3.8/site-packages` being produced in wrapper, which is wrong
Inspired by `wrapNeovim`, write a wrapMpv Nix function that creates a
derivation that has all of the environment that was added if needed at
the unwrapped version.
Add derivations to all-packages.nix in an almost compatible way and make
`mpv-with-scripts` throw a message implying to switch to `wrapMpv` which
has an incompatible signature.
Add to vapoursynth a new passthru attribute `python3` that is used in
passed down to the wrapper to ensure ABI compatibility with
`PYTHONPATH`.
Make sure mpris.so is stripped.
mpv-with-scripts: use a standard location for scripts in $out.
mpvScripts.convert: install to the new location of mpv scripts.
Replaced gobject-introspection dependency with glib.
