Deduplicate JUnit report filename validation

[Copilot]

The JUnit report command-line provider had drift-prone copies of the shared report filename/path validation logic, unlike the HTML and TRX providers which already delegate to ReportFileNameValidator. This change aligns JUnit with the shared validation path so future fixes and security-sensitive path checks apply consistently across report generators.

• Refactor JUnit command-line validation

  • Replace inline --report-junit-filename validation with ReportFileNameValidator.ValidateReportFileNameArgumentAsync(...)
  • Replace inline option cross-validation with ReportFileNameValidator.ValidateReportCommandLineOptionsAsync(...)

• Remove duplicated path-validation logic

  • Delete the JUnit-local copies of:
    • DirectorySeparators
    • EscapesResultsDirectory
    • IsPathFullyQualified

• Wire JUnit into shared helpers

  • Link src/Platform/SharedExtensionHelpers/ReportFileNameValidator.cs into Microsoft.Testing.Extensions.JUnitReport.csproj
  • This matches the existing HTML/TRX project structure

• Add focused JUnit command-line coverage

  • Add JUnitReportGeneratorCommandLineTests
  • Cover the same validation surface already exercised for HTML/TRX:
    • valid relative/absolute paths
    • invalid extension
    • empty filename
    • parent-directory traversal
    • Windows drive-relative paths
    • option dependency/discovery-mode validation

Example of the simplification:

public override Task<ValidationResult> ValidateOptionArgumentsAsync(CommandLineOption commandOption, string[] arguments)
    => commandOption.Name == JUnitReportFileNameOptionName
        ? global::Microsoft.Testing.Extensions.ReportFileNameValidator.ValidateReportFileNameArgumentAsync(
            arguments,
            ".xml",
            ExtensionResources.JUnitReportFileNameMustNotBeEmpty,
            ExtensionResources.JUnitReportFileNameExtensionIsNotXml,
            ExtensionResources.JUnitReportFileNameRelativePathMustStayUnderResultsDirectory)
        : ValidationResult.ValidTask;

[Copilot]

Pull request overview

This PR aligns the JUnit report extension’s command-line filename/path validation with the shared ReportFileNameValidator helper (already used by HTML/TRX), reducing drift and ensuring future fixes—especially around path safety checks—apply consistently across report generators.

Changes:

• Refactored JUnitReportGeneratorCommandLine to delegate filename and option cross-validation to Microsoft.Testing.Extensions.ReportFileNameValidator.
• Linked SharedExtensionHelpers/ReportFileNameValidator.cs into the JUnit report extension project to reuse the shared implementation.
• Added focused unit tests validating JUnit filename/path rules and option dependency/discovery-mode constraints.

Show a summary per file

File	Description
test/UnitTests/Microsoft.Testing.Extensions.UnitTests/Microsoft.Testing.Extensions.UnitTests.csproj	Adds a project reference to the JUnit report extension so its command-line provider can be exercised by unit tests.
test/UnitTests/Microsoft.Testing.Extensions.UnitTests/JUnitReportGeneratorCommandLineTests.cs	New unit tests covering JUnit report filename validation and command-line option cross-validation behaviors.
src/Platform/Microsoft.Testing.Extensions.JUnitReport/Microsoft.Testing.Extensions.JUnitReport.csproj	Links the shared ReportFileNameValidator helper into the JUnit extension to match HTML/TRX structure.
src/Platform/Microsoft.Testing.Extensions.JUnitReport/JUnitReportGeneratorCommandLine.cs	Replaces local validation logic with calls into the shared ReportFileNameValidator.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 0