Document MSIX package versioning

[Roy (RDMacLachlan)]

Summary

• documents four-part package version format and numeric comparison
• explains how versions control package updates
• provides preview-release and side-by-side identity strategies
• distinguishes non-Store flexibility from Microsoft Store requirements

Reviewed for technical accuracy by Howard Bot.

Fixes AB#35910379

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[learn-build-service-prod]

Learn Build status updates of commit 41f3235:

✅ Validation status: passed

File	Status	Preview URL	Details
msix-src/package/package-versioning.md	✅Succeeded
msix-src/toc.yml	✅Succeeded

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