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/development/libraries/allegro/5.nix

@@ -3,7 +3,7 @@
 , libXxf86dga, libXxf86misc
 , libXxf86vm, openal, libGLU, libGL, libjpeg, flac
 , libXi, libXfixes, freetype, libopus, libtheora
-, physfs, enet, pkgconfig, gtk2, pcre, libpulseaudio, libpthreadstubs
+, physfs, enet, pkg-config, gtk2, pcre, libpulseaudio, libpthreadstubs
 , libXdmcp
 }:
 
@@ -24,7 +24,7 @@ stdenv.mkDerivation rec {
     libXxf86vm openal libGLU libGL
     libjpeg flac
     libXi libXfixes
-    enet libtheora freetype physfs libopus pkgconfig gtk2 pcre libXdmcp
+    enet libtheora freetype physfs libopus pkg-config gtk2 pcre libXdmcp
     libpulseaudio libpthreadstubs
   ];