papirus-maia-icon-theme: add missing parent icon themes

Also:
- move postFixup actions to postInstallPhase

pkgs/data/icons/papirus-maia-icon-theme/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchFromGitHub, cmake, gtk3 }:
+{ stdenv, fetchFromGitHub, cmake, gtk3, breeze-icons, gnome-icon-theme, papirus-icon-theme, hicolor-icon-theme }:
 
 stdenv.mkDerivation rec {
   pname = "papirus-maia-icon-theme";
@@ -16,11 +16,20 @@ stdenv.mkDerivation rec {
     gtk3
   ];
 
+  propagatedBuildInputs = [
+    breeze-icons
+    gnome-icon-theme
+    papirus-icon-theme
+    hicolor-icon-theme
+  ];
+
+  dontDropIconThemeCache = true;
+
   postPatch = ''
     substituteInPlace CMakeLists.txt --replace /usr "$out"
   '';
 
-  postFixup = ''
+  postInstall = ''
     for theme in $out/share/icons/*; do
       gtk-update-icon-cache $theme
     done