Document breaking change: GnuTarEntry and PaxTarEntry no longer includes atime and ctime by default

[Copilot]

Added documentation for the breaking change introduced in .NET 10 Preview 5 where GnuTarEntry and PaxTarEntry no longer automatically set access time (atime) and change time (ctime) fields when creating new entries.

Changes Made

• Created new breaking change document: docs/core/compatibility/core-libraries/10.0/tar-atime-ctime-default.md

  • Documents the behavioral change with clear before/after descriptions
  • Explains the reason: better compatibility with tar readers that don't support these fields
  • Provides guidance for users who need these fields (they can set them explicitly)
  • Includes proper xref links to affected APIs

• Updated TOC: Added entry to docs/core/compatibility/toc.yml under Core .NET libraries section for .NET 10

• Updated index: Added entry to docs/core/compatibility/10.0.md in the Core .NET libraries table

Key Details

• Breaking change type: Behavioral change
• Version introduced: .NET 10 Preview 5
• Affected APIs:
  • System.Formats.Tar.GnuTarEntry
  • System.Formats.Tar.PaxTarEntry
  • System.Formats.Tar.TarReader
  • System.Formats.Tar.TarWriter

The documentation follows established patterns and maintains alphabetical ordering in both the TOC and index files. All changes pass markdownlint validation.

Fixes #46465.

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Internal previews

📄 File	🔗 Preview link
docs/core/compatibility/10.0.md	Breaking changes in .NET 10
docs/core/compatibility/core-libraries/10.0/tar-atime-ctime-default.md	GnuTarEntry and PaxTarEntry exclude atime and ctime by default
docs/core/compatibility/toc.yml	docs/core/compatibility/toc