feat(ui): add option to disable menu popup animations (#3737)

[leno23]

Summary

Fixes #3737.

Adds Enable menu animations to Display options (under Other). When unchecked, menu and submenu popups use PopupAnimation.None instead of the default fade-in.

• New installs default to the current OS menu animation preference.
• The setting is persisted in ILSpy.xml and applied at startup and when changed in options.

Test plan

• Open View → Options → Display and toggle Enable menu animations; open top-level menus and submenus (e.g. View → Theme) and confirm instant vs animated open.
• Restart ILSpy and confirm the preference is restored.
• CI build (no local .NET SDK in contributor environment; relying on GitHub Actions)

[siegfriedpammer]

Note

This comment was generated by Claude (claude-fable-5 via Claude Code) and is posted on its behalf after reading it.

Thanks for taking a look at #3737. We are closing this PR for two reasons:

1. It does not compile — the central API call is hallucinated. MenuPopupAnimationHelper.cs calls SystemParameters.OverrideMetadata(SystemParameters.MenuPopupAnimationKey, new FrameworkPropertyMetadata(...)), which does not exist in WPF: OverrideMetadata is a DependencyProperty method, and MenuPopupAnimationKey is a ResourceKey, not a dependency property. Building ILSpy/ILSpy.csproj at the PR head fails with CS0117. Please build before submitting; the repo compiles with TreatWarningsAsErrors, so anything that does not build locally cannot pass CI either.

2. It no longer applies — ILSpy's UI is now Avalonia, not WPF. This branch is based on a master from before the Avalonia 12 port landed; it patches files that no longer exist (App.xaml.cs, DisplaySettingsPanel.xaml, Util/SettingsService.cs) and relies on WPF-only concepts (SystemParameters, PopupAnimation) that have no Avalonia equivalent.