treewide: with stdenv.lib; in meta -> with lib;

Part of: https://github.com/NixOS/nixpkgs/issues/108938

meta = with stdenv.lib;

is a widely used pattern. We want to slowly remove
the `stdenv.lib` indirection and encourage people
to use `lib` directly. Thus let’s start with the meta
field.

This used a rewriting script to mostly automatically
replace all occurances of this pattern, and add the
`lib` argument to the package header if it doesn’t
exist yet.

The script in its current form is available at
https://cs.tvl.fyi/depot@2f807d7f141068d2d60676a89213eaa5353ca6e0/-/blob/users/Profpatsch/nixpkgs-rewriter/default.nix

pkgs/applications/misc/pdfdiff/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, pythonPackages, fetchurl, xpdf }:
+{ lib, stdenv, pythonPackages, fetchurl, xpdf }:
 let
   py = pythonPackages;
 in
@@ -32,7 +32,7 @@ py.buildPythonApplication rec {
     substituteInPlace $out/bin/pdfdiff --replace "#!/usr/bin/python" "#!${pythonPackages.python.interpreter}"
     '';
 
-  meta = with stdenv.lib; {
+  meta = with lib; {
     homepage = "http://www.cs.ox.ac.uk/people/cas.cremers/misc/pdfdiff.html";
     description = "Tool to view the difference between two PDF or PS files";
     license = licenses.gpl2Plus;