Add support for NUnitV3 content inside TouchUnit result files.

[rolfbjarne]

• Add a new TouchUnit_NUnitV3 xml result jargon.
• Refactor the TouchUnit test report generator to call into the NUnitV2 or NUnitV3 test report generators depending on the embedded content.
• Simplify the NUnitV3 test report generator to just look for 'test-case' elements, not caring about any parent nodes.
• Make the NUnitV3 test report print the full name of failing tests, not just the name.

[Copilot]

Pull Request Overview

This PR adds support for NUnitV3-formatted content within TouchUnit result files, previously only NUnitV2 format was supported. The implementation introduces a new TouchUnit_NUnitV3 XML result jargon while maintaining backward compatibility through an enum alias (TouchUnit_NUnitV2 = TouchUnit). The core change refactors the TouchUnitTestReportGenerator to detect the embedded format and delegate to the appropriate NUnitV2 or NUnitV3 test report generator, simplifying the code and eliminating duplication.

Key changes:

• Introduces TouchUnit_NUnitV3 enum value with backward-compatible alias for TouchUnit
• Detection logic in XmlResultParser distinguishes between TouchUnit variants based on presence of 'test-run' (NUnitV3) or 'test-results' (NUnitV2) elements
• NUnitV3TestReportGenerator simplified to iterate through all test-case elements using fullname instead of name for failed tests

Reviewed Changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/Microsoft.DotNet.XHarness.Common/XmlResultJargon.cs	Adds TouchUnit_NUnitV3 enum value and backward-compatible alias TouchUnit_NUnitV2 = TouchUnit
src/Microsoft.DotNet.XHarness.iOS.Shared/XmlResults/XmlResultParser.cs	Updates detection logic to distinguish between TouchUnit variants and adds both to the formatters dictionary
src/Microsoft.DotNet.XHarness.iOS.Shared/XmlResults/TouchUnitTestReportGenerator.cs	Refactored to delegate to NUnitV2 or NUnitV3 generators based on detected element name
src/Microsoft.DotNet.XHarness.iOS.Shared/XmlResults/NUnitV3TestReportGenerator.cs	Simplified to iterate all test-case elements directly; changed to use fullname attribute instead of name
src/Microsoft.DotNet.XHarness.iOS.Shared/XmlResults/NUnitV2TestReportGenerator.cs	Added check to handle reader already positioned at test-results element
tests/Microsoft.DotNet.XHarness.iOS.Shared.Tests/XmlResultParserTests.cs	Updated tests for new enum values and added two new test methods for TouchUnit report generation
tests/Microsoft.DotNet.XHarness.iOS.Shared.Tests/Microsoft.DotNet.XHarness.iOS.Shared.Tests.csproj	Added TouchUnitSample2.xml as embedded resource for testing