Refactor ANSI handling for better readability

[Youssef1313]

Sync with microsoft/testfx#7245

[Copilot]

Pull request overview

This PR refactors ANSI handling in the terminal test reporter by replacing two boolean flags (UseAnsi and UseCIAnsi) with a single, more expressive AnsiMode enum. This change improves code readability and maintainability by making the different ANSI modes explicit.

Changes:

• Introduced AnsiMode enum with four values: NoAnsi, SimpleAnsi, AnsiIfPossible, and ForceAnsi
• Replaced boolean properties UseAnsi and UseCIAnsi in TerminalTestReporterOptions with AnsiMode property
• Updated TerminalTestReporter constructor to use the new enum for clearer logic flow
• Modified MicrosoftTestingPlatformTestCommand to map command-line flags and CI detection to appropriate AnsiMode values

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/Cli/dotnet/Commands/Test/MTP/Terminal/TerminalTestReporterOptions.cs	Replaced boolean properties with AnsiMode enum; added well-documented AnsiMode enum with four values
src/Cli/dotnet/Commands/Test/MTP/Terminal/TerminalTestReporter.cs	Refactored constructor logic to use AnsiMode enum instead of booleans; simplified branching logic
src/Cli/dotnet/Commands/Test/MTP/MicrosoftTestingPlatformTestCommand.cs	Updated initialization logic to map --no-ansi flag and CI detection to AnsiMode values

[Youssef1313]

/backport to release/10.0.2xx

[github-actions]

Started backporting to release/10.0.2xx (link to workflow run)