kde6Packages.sddm: split unwrapped build out of wrapper expression

This makes overlaying sddm somewhat easier. Before:

  (self: super: {
    qt6Packages = super.qt6Packages.overrideScope (qtself: qtsuper: {
      sddm = qtsuper.sddm.override (o: {
        unwrapped = qtsuper.sddm.unwrapped.overrideAttrs (o: {
          patches = o.patches ++ [./sddm.patch];
        });
      });
    });
  })

After:

  (self: super: {
    qt6Packages = super.qt6Packages.overrideScope (qtself: qtsuper: {
      sddm-unwrapped = qtsuper.sddm-unwrapped.overrideAttrs (o: {
        patches = o.patches ++ [./sddm.patch];
      });
    })
  })

pkgs/applications/display-managers/sddm/default.nix

@@ -3,41 +3,41 @@
   callPackage,
   runCommand,
   wrapQtAppsHook,
-  unwrapped ? callPackage ./unwrapped.nix { },
+  sddm-unwrapped,
   extraPackages ? [ ],
 }:
 runCommand "sddm-wrapped"
   {
-    inherit (unwrapped) version outputs;
+    inherit (sddm-unwrapped) version outputs;
 
-    buildInputs = unwrapped.buildInputs ++ extraPackages;
+    buildInputs = sddm-unwrapped.buildInputs ++ extraPackages;
     nativeBuildInputs = [ wrapQtAppsHook ];
 
     strictDeps = true;
 
     passthru = {
-      inherit unwrapped;
-      inherit (unwrapped.passthru) tests;
+      unwrapped = sddm-unwrapped;
+      inherit (sddm-unwrapped.passthru) tests;
     };
 
-    meta = unwrapped.meta;
+    meta = sddm-unwrapped.meta;
   }
   ''
     mkdir -p $out/bin
 
-    cd ${unwrapped}
+    cd ${sddm-unwrapped}
 
     for i in *; do
       if [ "$i" == "bin" ]; then
         continue
       fi
-      ln -s ${unwrapped}/$i $out/$i
+      ln -s ${sddm-unwrapped}/$i $out/$i
     done
 
     for i in bin/*; do
-      makeQtWrapper ${unwrapped}/$i $out/$i --set SDDM_GREETER_DIR $out/bin
+      makeQtWrapper ${sddm-unwrapped}/$i $out/$i --set SDDM_GREETER_DIR $out/bin
     done
 
     mkdir -p $man
-    ln -s ${lib.getMan unwrapped}/* $man/
+    ln -s ${lib.getMan sddm-unwrapped}/* $man/
   ''

pkgs/top-level/qt6-packages.nix

@@ -138,6 +138,7 @@ makeScopeWithSplicing' {
         callPackage ../development/libraries/sailfish-access-control-plugin
           { };
 
+      sddm-unwrapped = kdePackages.callPackage ../applications/display-managers/sddm/unwrapped.nix { };
       sddm = kdePackages.callPackage ../applications/display-managers/sddm { };
 
       sierra-breeze-enhanced =