icu: Add `meta.pkgConfigModules` and test

pkgs/development/libraries/icu/63.nix

···
-{ stdenv, lib, fetchurl, fetchpatch, fixDarwinDylibNames, nativeBuildRoot, buildRootOnly ? false }:
+{ stdenv, lib, fetchurl, fetchpatch, fixDarwinDylibNames, nativeBuildRoot, testers
+, buildRootOnly ? false
+}:
 
 import ./base.nix {
   version = "63.1";
···
     })
   ];
   patchFlags = [ "-p3" ];
-} { inherit stdenv lib fetchurl fixDarwinDylibNames nativeBuildRoot buildRootOnly; }
+} { inherit stdenv lib fetchurl fixDarwinDylibNames nativeBuildRoot testers buildRootOnly; }

pkgs/development/libraries/icu/base.nix

···
 { stdenv, lib, fetchurl, fixDarwinDylibNames
   # Cross-compiled icu4c requires a build-root of a native compile
 , buildRootOnly ? false, nativeBuildRoot
+, testers
 }:
 
 let
···
       description = "Unicode and globalization support library";
       homepage = "https://icu.unicode.org/";
       maintainers = with maintainers; [ raskin ];
+      pkgConfigModules = [
+        "icu-i18n"
+        "icu-io"
+        "icu-uc"
+      ];
       platforms = platforms.all;
     };
   };
···
             then buildRootOnlyAttrs
           else realAttrs;
 in
-stdenv.mkDerivation attrs
+stdenv.mkDerivation (finalAttrs: attrs // {
+  passthru.tests.pkg-config = testers.testMetaPkgConfig finalAttrs.finalPackage;
+})