treewide: handle *Phases variables __structuredAttrs-agnostically (round 2) (#352709)

pkgs/build-support/dotnet/build-dotnet-module/hooks/dotnet-fixup-hook.sh

···
 }
 
 if [[ -z "${dontFixup-}" && -z "${dontDotnetFixup-}" ]]; then
-    preFixupPhases+=" dotnetFixupHook"
+    appendToVar preFixupPhases dotnetFixupHook
 fi

pkgs/build-support/setup-hooks/wrap-gapps-hook/wrap-gapps-hook.sh

···
     done
 }
 
-preFixupPhases+=" gappsWrapperArgsHook"
+appendToVar preFixupPhases gappsWrapperArgsHook
 
 wrapGApp() {
     local program="$1"

pkgs/by-name/de/desktop-file-utils/setup-hook.sh

···
     rm -f $out/share/applications/mimeinfo.cache
 }
 
-preFixupPhases="${preFixupPhases-} mimeinfoPreFixupPhase"
+appendToVar preFixupPhases mimeinfoPreFixupPhase

pkgs/development/ada-modules/gprbuild/gpr-project-darwin-rpath-hook.sh

···
     done
 }
 
-preFixupPhases+=" fixGprProjectDarwinRpath"
+appendToVar preFixupPhases fixGprProjectDarwinRpath

pkgs/development/libraries/gtk/hooks/drop-icon-theme-cache.sh

···
     fi
 }
 
-preFixupPhases="${preFixupPhases-} dropIconThemeCache"
+appendToVar preFixupPhases dropIconThemeCache

pkgs/development/libraries/qt-5/hooks/wrap-qt-apps-hook.sh

···
     qtHostPathHook "${!outputBin}"
 }
 
-preFixupPhases+=" qtOwnPathsHook"
+appendToVar preFixupPhases qtOwnPathsHook
 
 # Note: $qtWrapperArgs still gets defined even if ${dontWrapQtApps-} is set.
 wrapQtAppsHook() {

pkgs/development/libraries/qt-6/hooks/wrap-qt-apps-hook.sh

···
         qtHostPathHook "${!outputBin}"
     }
 
-    preFixupPhases+=" qtOwnPathsHook"
+    appendToVar preFixupPhases qtOwnPathsHook
 
     # Note: $qtWrapperArgs still gets defined even if ${dontWrapQtApps-} is set.
     wrapQtAppsHook() {