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/gstreamer/core/default.nix

@@ -2,7 +2,7 @@
 , fetchurl
 , meson
 , ninja
-, pkgconfig
+, pkg-config
 , gettext
 , gobject-introspection
 , bison
@@ -44,7 +44,7 @@ stdenv.mkDerivation rec {
   nativeBuildInputs = [
     meson
     ninja
-    pkgconfig
+    pkg-config
     gettext
     bison
     flex
@@ -77,7 +77,7 @@ stdenv.mkDerivation rec {
     "-Dexamples=disabled" # requires many dependencies and probably not useful for our users
     "-Ddoc=disabled" # `hotdoc` not packaged in nixpkgs as of writing
   ] ++ lib.optionals stdenv.isDarwin [
-    # darwin.libunwind doesn't have pkgconfig definitions so meson doesn't detect it.
+    # darwin.libunwind doesn't have pkg-config definitions so meson doesn't detect it.
     "-Dlibunwind=disabled"
     "-Dlibdw=disabled"
   ];