Add IdnMapping.GetAscii and currency symbol behavioral difference examples to ICU globalization breaking change

[Copilot]

The .NET 5 ICU globalization breaking change article lacked concrete behavioral examples showing how switching from NLS to ICU affects real-world code.

Changes

• Added IdnMapping.GetAscii example — ICU lowercases all domain name labels as part of ACE processing; NLS preserves casing for ASCII-only input:

  var mapping = new System.Globalization.IdnMapping();
  string asciiName = mapping.GetAscii("ABCDEFG");
  // .NET Core 3.1 (NLS): "ABCDEFG"
  // .NET 5+ on Windows 19H1+ (ICU): "abcdefg"

• The currency symbol example (CultureInfo("de") + {0:C} → ¤ instead of €) was already present in the file—no change needed there.

• Updated ms.date and added ai-usage: ai-assisted frontmatter per repo conventions.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update globalization breaking change with examples</issue_title>
<issue_description>Update https://docs.microsoft.com/en-us/dotnet/core/compatibility/3.1-5.0#globalization-apis-use-icu-libraries-on-windows with practical examples of issues that users might see, for example:

• Currency symbol
• Internet domain name mapping

---

Document Details

⚠ Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.

• ID: 5f68af3a-3848-48ef-c24b-cf33b880ca1b
• Version Independent ID: 580c061d-20e5-248c-a24f-7a48a684c7e3
• Content: Breaking changes, version 3.1 to 5.0 - .NET Core
• Content Source: docs/core/compatibility/3.1-5.0.md
• Product: dotnet-core
• GitHub Login: @gewarren
• Microsoft Alias: gewarren</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Update globalization breaking change with examples #19718

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docs/core/compatibility/globalization/5.0/icu-globalization-api.md	docs/core/compatibility/globalization/5.0/icu-globalization-api