Feature request: Expand the `MenuFlyout` example in `reactor-gallery`

Nobody has claimed this yet.

### Suggestion

The current `MenuFlyout` page in the Rust `reactor-gallery` sample only demonstrates two basic usage scenarios: a `MenuFlyout` with standard menu items, and a `MenuFlyout` with standard menu items and a separator.

It would be useful to expand this page into a more complete `MenuFlyout` showcase, similar to the `MenuFlyout` page in the WinUI 3 Gallery.

The goal is to demonstrate the different `MenuFlyout` capabilities and usage patterns that are available in WinUI 3, rather than only showing the most basic cases.

Specifically, I would like the `reactor-gallery` `MenuFlyout` page to include examples for:

* A `MenuFlyout` with `ToggleMenuFlyoutItems` and `MenuFlyoutSeparator`.
* A `MenuFlyout` with cascading menus.
* A `MenuFlyout` with `SplitMenuFlyoutItems`.
* A `MenuFlyout` with icons.
* A `MenuFlyout` with icons and Keyboard Accelerators.
* A `MenuFlyout` with `RadioMenuFlyoutItems`.

Ideally, the Rust `reactor-gallery` page would provide a similar set of interactive examples and overall presentation to the corresponding `MenuFlyout` page in the WinUI 3 Gallery.

I will attach a video to this issue showing the `MenuFlyout` page in the WinUI 3 Gallery as a visual reference for the desired result.

This would make the `reactor-gallery` example much more useful as a reference for Rust developers learning how to use `MenuFlyout` and its different item types with `windows-reactor`.

Thank you!

https://github.com/user-attachments/assets/f2b2d851-0c67-4fcd-ac16-0b8621ba2c2f

Start with the existing MenuFlyout page in the Rust reactor-gallery sample and compare its two current scenarios with the corresponding MenuFlyout page in the WinUI 3 Gallery. Done means adding interactive examples for toggle items and separators, cascading menus, split items, icons, icons with keyboard accelerators, and radio items.

Written by the indexing model from the issue text.