Update x:Load attribute documentation

[hoshiizumiya]

Clarified restrictions and usage notes for x:Load attribute, including details on x:Bind interactions and error handling.

[prmerger-automator]

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[learn-build-service-prod]

Learn Build status updates of commit d693e80:

✅ Validation status: passed

File	Status	Preview URL	Details
hub/apps/develop/platform/xaml/x-load-attribute.md	✅Succeeded

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[Copilot]

Pull request overview

This PR updates the x:Load attribute documentation to clarify platform-specific restrictions (notably WinUI 3 Window root scenarios) and to add guidance about x:Bind interactions and known C++/WinRT limitations.

Changes:

• Added a CAUTION note about FindName behavior when the XAML root element is a WinUI 3 Window.
• Expanded x:Bind guidance to mention a naming collision that can trigger XAML compiler errors.
• Added new “Restrictions” bullets linking to known C++/WinRT issues/workarounds.

[learn-build-service-prod]

Learn Build status updates of commit efc0661:

✅ Validation status: passed

File	Status	Preview URL	Details
hub/apps/develop/platform/xaml/x-load-attribute.md	✅Succeeded

For more details, please refer to the build report.

[learn-build-service-prod]

Learn Build status updates of commit 8551a12:

✅ Validation status: passed

File	Status	Preview URL	Details
hub/apps/develop/platform/xaml/x-load-attribute.md	✅Succeeded

For more details, please refer to the build report.