Preserve supplementary Unicode in TRX reports

[Copilot]

TrxReport escaped valid supplementary Unicode characters, such as emoji, as separate surrogate literals (\uD83D\uDE00). XML 1.0 allows these characters when represented as well-formed surrogate pairs, so report content lost the original text.

• Sanitization

  • Replaced UTF-16 code-unit regex sanitization with a scanner that preserves valid surrogate pairs.
  • Continues escaping invalid XML code units, including unpaired surrogates, as \uXXXX.

• Regression coverage

  • Added TRX tests for preserving supplementary Unicode in display names, stdout, exception messages, and stack traces.
  • Added coverage for escaping unpaired surrogate code units.

Example behavior:

"stdout 😀"        // preserved in TRX
"stdout \uD800"   // emitted as "stdout \\ud800"

[Amaury Levé (Evangelink)]

Keeping the existing pattern used throughout this file (e.g. lines 45-46, 66-67, 92-93, ...): Assert.IsNotNull(memoryStream.TrxContent); followed by XDocument xml = memoryStream.TrxContent;. MSTest's Assert.IsNotNull is annotated with [NotNull], so the compiler's null-state analysis flows through and there is no CS warning. Adding ! only on the two new tests would diverge from the established convention in this file.

[Copilot]

Pull request overview

This pull request updates TRX sanitization to preserve valid supplementary Unicode characters (e.g., emoji) in generated TRX XML while still escaping invalid XML UTF-16 code units (including unpaired surrogates) as \uXXXX, preventing loss of original text in report content.

Changes:

• Replaced regex-based XML character sanitization with a UTF-16 scanner that preserves well-formed surrogate pairs.
• Added unit tests verifying supplementary Unicode is preserved in TRX attributes/elements and that unpaired surrogates are escaped.

Show a summary per file

File	Description
test/UnitTests/Microsoft.Testing.Extensions.UnitTests/TrxTests.cs	Adds regression tests for preserved supplementary Unicode and escaped unpaired surrogates in TRX output.
src/Platform/Microsoft.Testing.Extensions.TrxReport/TrxReportEngine.Utilities.cs	Reworks XML sanitization to retain valid surrogate pairs while escaping invalid UTF-16 code units.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 0