treewide: pkgs.pkgconfig -> pkgs.pkg-config, move pkgconfig to alias.nix

continuation of #109595

pkgconfig was aliased in 2018, however, it remained in
all-packages.nix due to its wide usage. This cleans
up the remaining references to pkgs.pkgsconfig and
moves the entry to aliases.nix.

python3Packages.pkgconfig remained unchanged because
it's the canonical name of the upstream package
on pypi.

pkgs/applications/audio/x42-plugins/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchurl, pkgconfig
+{ lib, stdenv, fetchurl, pkg-config
 , libltc, libsndfile, libsamplerate, ftgl, freefont_ttf, libjack2
 , libGLU, lv2, gtk2, cairo, pango, fftwFloat, zita-convolver }:
 
@@ -11,7 +11,7 @@ stdenv.mkDerivation rec {
     sha256 = "1av05ykph8x67018hm9zfgh1vk0zi39mvrsxkj6bm4hkarxf0vvl";
   };
 
-  nativeBuildInputs = [ pkgconfig ];
+  nativeBuildInputs = [ pkg-config ];
   buildInputs = [ libGLU ftgl freefont_ttf libjack2 libltc libsndfile libsamplerate lv2 gtk2 cairo pango fftwFloat zita-convolver ];
 
   # Don't remove this. The default fails with 'do not know how to unpack source archive'