Document XsltSettings.EnableScript property obsolescence in .NET 10

[Copilot]

This PR adds comprehensive breaking change documentation for the System.Xml.Xsl.XsltSettings.EnableScript property being marked as obsolete with diagnostic ID SYSLIB0062 in .NET 10.

Changes Made

Breaking Change Documentation

• New document: docs/core/compatibility/xml/10.0/xsltsettings-enablescript-obsolete.md
  • Documents the obsoletion with proper metadata and frontmatter
  • Explains version introduced (.NET 10 Preview 1), previous vs. new behavior
  • Provides clear migration guidance for developers
  • Follows the established breaking change template format

Documentation Updates

• Updated TOC: Added XML and XSLT section to .NET 10 compatibility documentation
• Updated index: Added entry to the main breaking changes index for .NET 10
• Enhanced existing docs:
  • Added warning in script-blocks-using-msxsl-script.md about the obsoletion
  • Added note in code analysis rule ca3076.md about the property being obsolete

Code Sample Updates

• Updated C# and VB.NET sample files to include warnings about EnableScript being obsolete
• Added comments for both property assignment and constructor usage patterns
• Maintained backward compatibility while alerting developers to the upcoming change

Context

XSLT script blocks are only supported in .NET Framework and have never worked on .NET Core or .NET 5+. The EnableScript property had no legitimate use case on modern .NET:

• When set to false: simply skips script blocks (expected behavior)
• When set to true: throws PlatformNotSupportedException at runtime

Obsoleting this API converts a runtime error into a build-time warning, providing better developer guidance.

Fixes #47504.

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Internal previews

📄 File	🔗 Preview link
docs/core/compatibility/core-libraries/10.0/obsolete-apis.md	API obsoletions with non-default diagnostic IDs (.NET 10)
docs/core/compatibility/unsupported-apis.md	Unsupported APIs on .NET Core and .NET 5+
docs/fundamentals/code-analysis/quality-rules/ca3076.md	CA3076: Insecure XSLT Script Execution
docs/fundamentals/syslib-diagnostics/obsoletions-overview.md	docs/fundamentals/syslib-diagnostics/obsoletions-overview
docs/fundamentals/syslib-diagnostics/syslib0061.md	SYSLIB0061: System.Linq.Queryable.MaxBy and System.Linq.Queryable.MinBy taking an IComparer<TSource> are obsolete
docs/fundamentals/syslib-diagnostics/syslib0062.md	SYSLIB0062 warning - XsltSettings.EnableScript is obsolete
docs/navigate/tools-diagnostics/toc.yml	docs/navigate/tools-diagnostics/toc
docs/standard/data/xml/script-blocks-using-msxsl-script.md	Script blocks Using msxsl:script

[BillWagner]

This LGTM @gewarren