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/servers/rainloop/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, unzip, pkgs, dataPath ? "/var/lib/rainloop" }: let
+{ lib, stdenv, fetchurl, unzip, pkgs, dataPath ? "/var/lib/rainloop" }: let
   common = { edition, sha256 }:
     stdenv.mkDerivation (rec {
       pname = "rainloop${stdenv.lib.optionalString (edition != "") "-${edition}"}";
@@ -38,7 +38,7 @@
         chmod 700 $out/data
       '';
 
-      meta = with stdenv.lib; {
+      meta = with lib; {
         description = "Simple, modern & fast web-based email client";
         homepage = "https://www.rainloop.net";
         downloadPage = "https://github.com/RainLoop/rainloop-webmail/releases";