Add StreamMediaSource documentation

[matt-goldman]

I have added StreamMediaSource to the .NET MAUI CommunityToolkit MediaElement, which allows media playback from stream (in addition to the existing embedded, file, and URL sources).

This documentation update adds this to the existing MediaElement documentation page.

[learn-build-service-prod]

Learn Build status updates of commit 124bf32:

💡 Validation status: suggestions

File	Status	Preview URL	Details
docs/maui/views/MediaElement.md	💡Suggestion	View	Details

docs/maui/views/MediaElement.md

• Line 247, Column 46: [Suggestion: docs-link-absolute - See documentation] Absolute link 'https://learn.microsoft.com/dotnet/maui/platform-integration/device-media/picker' will be broken in isolated environments. Replace with a relative link.

For more details, please refer to the build report.

Note: Your PR may contain errors or warnings or suggestions unrelated to the files you changed. This happens when external dependencies like GitHub alias, Microsoft alias, cross repo links are updated. Please use these instructions to resolve them.

[learn-build-service-prod]

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[learn-build-service-prod]

PoliCheck Scan Report

The following report lists PoliCheck issues in PR files. Before you merge the PR, you must fix all severity-1 and severity-2 issues. The AI Review Details column lists suggestions for either removing or replacing the terms. If you find a false positive result, mention it in a PR comment and include this text: #policheck-false-positive. This feedback helps reduce false positives in future scans.

✅ No issues found

More information about PoliCheck

Information: PoliCheck | Severity Guidance | Term
For any questions: Try searching the learn.microsoft.com contributor guides or post your question in the Learn support channel.

[learn-build-service-prod]

Learn Build status updates of commit f59064f:

💡 Validation status: suggestions

File	Status	Preview URL	Details
docs/maui/views/MediaElement.md	💡Suggestion	View	Details

docs/maui/views/MediaElement.md

• Line 247, Column 46: [Suggestion: docs-link-absolute - See documentation] Absolute link 'https://learn.microsoft.com/dotnet/maui/platform-integration/device-media/picker' will be broken in isolated environments. Replace with a relative link.

For more details, please refer to the build report.

Note: Your PR may contain errors or warnings or suggestions unrelated to the files you changed. This happens when external dependencies like GitHub alias, Microsoft alias, cross repo links are updated. Please use these instructions to resolve them.