fix: Fallback from Segoe UI Symbol to configured symbol font

[MartinZikmund]

GitHub Issue: closes #4579

PR Type: 🐞 Bugfix

What is the current behavior? 🤔

What is the new behavior? 🚀

PR Checklist ✅

Please check if your PR fulfills the following requirements:

• 📝 Commits must be following the Conventional Commits specification.
• 🧪 Added Runtime tests, UI tests, or a manual test sample for the changes have been added (for bug fixes / features) (if applicable)
• 📚 Docs have been added/updated which fit documentation template (for bug fixes / features)
• 🖼️ Validated PR Screenshots Compare Test Run results.
• ❗ Contains NO breaking changes

Other information ℹ️

[Copilot]

Pull Request Overview

This PR adds missing fallback support for the "Segoe UI Symbol" font in FontFamily and introduces a unit test to verify symbol font fallback behavior.

• Extend the font fallback condition in FontFamily to include "Segoe UI Symbol"
• Refactor unit tests: narrow the WASM guard and add a new Symbol_Fonts_Fallback test

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/Uno.UI/UI/Xaml/FontFamily.cs	Added a Contains("Segoe UI Symbol") check alongside existing symbol font conditions
src/Uno.UI.RuntimeTests/.../Given_FontFamily.cs	Updated test scaffold: wrapped only the pure-name test in #if __WASM__, added a fallback test

Comments suppressed due to low confidence (2)

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Media/Given_FontFamily.cs:61

• Add additional test cases where the family name contains the symbol font as part of a path or file name (e.g., "fonts/Segoe UI Symbol.ttf") to ensure the Contains logic correctly triggers fallback in non-exact-match scenarios.

			fontFamily = new FontFamily("Segoe UI Symbol");

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Media/Given_FontFamily.cs:57

• [nitpick] Consider renaming this test to something more descriptive, e.g. Fallback_When_FontFamilyIsSymbolFont, to clearly convey the scenario being validated.

		public void Symbol_Fonts_Fallback()

[unodevops]

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[unodevops]

🤖 Your WebAssembly Skia Sample App stage site is ready! Visit it here: https://unowasmprstaging.z20.web.core.windows.net/pr-21070/wasm-skia-net9/index.html

[unodevops]

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[unodevops]

⚠️⚠️ The build 171372 has failed on Uno.UI - CI.

[unodevops]

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-21070/docs/index.html

[unodevops]

🤖 Your WebAssembly Skia Sample App stage site is ready! Visit it here: https://unowasmprstaging.z20.web.core.windows.net/pr-21070/wasm-skia-net9/index.html

[MartinZikmund]

Keeping open until new text rendering changes are merged, after which it will need to be adjusted

cc @ramezgerges

[unodevops]

⚠️⚠️ The build 171476 has failed on Uno.UI - CI.