`Flyout` should not be stretched horizontally on large screen

[dr1rrb]

Current behavior

When adding

<MaterialToolkitTheme xmlns="using:Uno.Toolkit.UI.Material"
			ColorOverrideSource="ms-appx:///unoExtensionBasicApp/Styles/ColorPaletteOverride.xaml"
			FontOverrideSource="ms-appx:///unoExtensionBasicApp/Styles/MaterialFontsOverride.xaml" />

you are able to have Flyout stretch horizontally on large screen apps, while on Windows default style has a hard-coded maximum width that prevents this behavior (the Flyout will be full-screen on small devices and only "above the content" on "large window").

This is causing some issues like https://github.com/unoplatform/uno/issues/12871

Expected behavior

Like the default style on windows, the Flyout should have a max width.

How to reproduce it (as minimally and precisely as possible)

cf. repro of https://github.com/unoplatform/uno/issues/12871

Nuget Package: Package Version(s): Affected platform(s):

• [x] WebAssembly
• [ ] Android
• [ ] iOS
• [ ] macOS (AppKit)
• [ ] Mac Catalyst
• [x] Skia
  • [x] WPF
  • [x] GTK (Linux)
  • [x] Linux Framebuffer
  • [x] Tizen
• [x] Windows

IDE:

• [ ] Visual Studio 2022
• [ ] Visual Studio 2019
• [ ] Visual Studio Code
• [ ] Visual Studio for Mac
• [ ] Rider Windows
• [ ] Rider macOS

Relevant plugins:

Anything else we need to know?

I was unable to repro that issue in a simpler app, not even sure how / why the Flyout is stretching like that.

[dr1rrb]

So thanks to @kazo0 , I found that this is actually caused by https://github.com/unoplatform/Uno.Themes/blob/321b2154bc547e0b3202cca160b2def25d3b3685/src/library/Uno.Material/Styles/Controls/v2/Flyout.xaml#L37

This should be reviewed with design, but IMHO we should not do that as it goes against Window's behavior (which applies a MaxWidth on large screen).