Refactor ANSI handling for better readability

[Youssef1313]

Keeping three boolean properties for ANSI handling (UseAnsi, ForceAnsi, UseCIAnsi) is IMO unnecessarily complicated. It creates 8 possible combinations, while in reality we have just 4 possibilities (one of them is test-only).

This refactors the three properties to be a single property of a new enum type that can be NoAnsi, SimpleAnsi, AnsiIfPossible, ForceAnsi.

• NoAnsi: disable both coloring and cursor movement. User requests it explicitly via --no-ansi
• SimpleAnsi: enables only coloring. Used in CI, unless the user specifies --no-ansi.
• AnsiIfPossible: Enables both coloring and cursor movement, but only if we detect that the terminal is capable.
• ForceAnsi: Used only by unit tests. Force-enables coloring and cursor movement, even if terminal isn't capable.

[Copilot]

Pull request overview

This PR refactors ANSI handling from three boolean properties (UseAnsi, ForceAnsi, UseCIAnsi) to a single enum property (AnsiMode) with four clearly defined values, significantly improving code clarity and maintainability.

Changes:

• Introduced AnsiMode enum with four values: NoAnsi, SimpleAnsi, AnsiIfPossible, and ForceAnsi
• Refactored TerminalTestReporterOptions to use the new AnsiMode enum instead of three boolean properties
• Updated TerminalTestReporter constructor logic to handle the new enum-based approach
• Updated TerminalOutputDevice to set the appropriate AnsiMode based on command-line options and CI detection
• Updated all test cases to use the new AnsiMode enum values

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/Platform/Microsoft.Testing.Platform/OutputDevice/Terminal/TerminalTestReporterOptions.cs	Replaced three boolean properties with a single AnsiMode enum property; added the AnsiMode enum with four well-documented values
src/Platform/Microsoft.Testing.Platform/OutputDevice/Terminal/TerminalTestReporter.cs	Refactored constructor logic to use AnsiMode enum with cleaner conditional flow
src/Platform/Microsoft.Testing.Platform/OutputDevice/TerminalOutputDevice.cs	Updated initialization logic to determine and set the appropriate AnsiMode based on command-line options and CI detection
test/UnitTests/Microsoft.Testing.Platform.UnitTests/OutputDevice/Terminal/TerminalTestReporterTests.cs	Updated all test cases to use the new AnsiMode enum values instead of multiple boolean properties