mpv: Move all wrappings to a single wrapper Nix function

[doronbehar]

Motivation for this change

In #88136 I concluded that mpv's wrapping was done purely - both the "unwrapped" build had done some wrappings to the two executables in $out/bin/, while we already had an external wrapper derivation called mpv-with-scripts. This was bad because:

1. Users of mpv-with-scripts had their executable wrapped twice.
2. disabling youtubeSupport caused mpv to be wrapped twice while it was a mere change of including youtube-dl in the wrapper's $PATH or not.
3. If you'd want youtubeSupport enabled, but say you had an override for an updated youtube-dl, it was impossible to make mpv use your youtube-dl without recompiling it.

Things done

This PR is a rewrite of what was called mpv-with-scripts - it's now called wrapMpv (inspired by Neovim's wrapNeovim Nix function) and it's possible with it to satisfy both "deterministics" which want everything to be configured exactly as they want via Nix while it enables everyone to tweak what's possible via an external wrapper which doesn't trigger a rebuild of mpv.

I tested wrapMpv with:

• mpv-unwrapped was compiled with and without vapoursynthSupport enabled - checked that the wrapper got the same environment but:
  • I haven't tested functionality of this feature.
• A certain script - checked that the necessary flags are added to the wrapper and also tested that the script works.
• Tested that youtubeSupport works (of course it works as the exectuable has the same environment).

Besides that, as always:

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

cc @pstch @AndersonTorres @jtojnar

[doronbehar]

@GrahamcOfBorg build mpv-unwrapped

@GrahamcOfBorg build mpv

[doronbehar]

Is it me or do these build commands don't work? :/

[ajs124]

They only work if you're a whitelisted user.

[doronbehar]

I am - https://github.com/NixOS/ofborg/blob/released/config.public.json#L36

[AndersonTorres]

Just looking from above, feels good to me, and way more organized.
Pushing out the wrap logic is a great improvement.

[teto]

It's more inline with current nixpkgs' approach.

[Profpatsch]

It would be great if symbols like mpv-with-wrappers would get a deprecation period instead of breaking downstream immediately.

Since this is a breaking change, this requires an entry in the release notes cc @doronbehar @AndersonTorres

[doronbehar]

You are correct. It was on my mind, I wanted to get some feedback before adding to the PR the changes to rl-2009 but I forgot about it after a while. See: #89208