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/libextractor/default.nix

@@ -1,6 +1,6 @@
 { fetchurl, stdenv, substituteAll
 , libtool, gettext, zlib, bzip2, flac, libvorbis
-, exiv2, libgsf, rpm, pkgconfig, fetchpatch
+, exiv2, libgsf, rpm, pkg-config, fetchpatch
 , gstreamerSupport ? true, gst_all_1 ? null
 # ^ Needed e.g. for proper id3 and FLAC support.
 #   Set to `false` to decrease package closure size by about 87 MB (53%).
@@ -61,7 +61,7 @@ stdenv.mkDerivation rec {
   buildInputs =
    [ libtool gettext zlib bzip2 flac libvorbis exiv2
      libgsf rpm
-     pkgconfig
+     pkg-config
    ] ++ stdenv.lib.optionals gstreamerSupport
           ([ gst_all_1.gstreamer ] ++ gstPlugins gst_all_1)
      ++ stdenv.lib.optionals gtkSupport [ glib gtk3 ]