Document direct property assignment using ms-resource URI scheme for UWP string resources

[Copilot]

This PR adds documentation for directly assigning resource strings to XAML properties using the ms-resource URI scheme, addressing a gap in the current localization documentation.

Previously, the documentation only covered using the x:Uid directive for implicit property binding:

<TextBlock x:Uid="Greeting"/>

This change adds a new subsection "Direct property assignment using ms-resource" that explains how to explicitly assign resource strings to properties:

<TextBlock Text="ms-resource:///Resources/Farewell"/>

The new documentation covers:

• Basic syntax for referencing string resources: ms-resource:///Resources/ResourceIdentifier
• Examples for different resource files: ms-resource:///ErrorMessages/PasswordTooWeak
• When to use direct assignment vs. the implicit x:Uid approach
• Clear explanation that this provides more explicit control over resource assignment

This directly answers the user's question about what syntax to use for <TextBlock Text="{WHAT DO I PUT HERE TO GET RESOURCE STRING}" />.

Fixes #4724.

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[dotMorten]

@alvinashcraft I was about to call you lazy :), but if the PR it made is correct (will have to test), I'm honestly impressed

[dotMorten]

This approach described does not work

[dotMorten]

This of course doesn't work, since you can't place a Uri in a Text property. It would just write the text ms-resource:///ErrorMessages/PasswordTooWeak

[alvinashcraft]

Yep, you're correct. I wonder where the model is interpreting this info from. If I do a similar Bing search, the Copilot answer in my search results also tells me to do this. It's got the same example where it assigns it to the Text property.

[dotMorten]

The closest I've found an answer is this UWP answer: https://devblogs.microsoft.com/ifdef-windows/use-a-custom-resource-markup-extension-to-succeed-at-ui-string-globalization/
But first of all it doesn't work in WinUI 3 (sigh), and second, forcing you to set a global static property might work at the app level, but is completely broken for any class library trying to use resources, since there can be only one.

So far I've resorted to a custom markup extension but it really shouldn't be this hard to get resources into xaml.

[dotMorten]

I'm guessing it is getting it from here: https://learn.microsoft.com/en-us/windows/uwp/app-resources/uri-schemes#scheme-name-ms-resource

[alvinashcraft]

Must be. Well, I'm going to just close this PR and run the question by some folks on the product team to see if there are any other ideas. If not, it should probably be added as a feature request for WinUI/WASDK.

[dotMorten]

it should probably be added as a feature request for WinUI/WASDK.

Aw man... they are getting tired of me doing that 😀

[alvinashcraft]

There's a NamedResource class in UWP/WinRT. I wonder if something like that would work if it were ported to WinAppSDK. You can set an ms-resource in its Uri property.