Add tests for help in dotnet test

[mariam-abdulla]

This pull request includes several updates to the test/dotnet-test.Tests/GivenDotnetTestBuildsAndRunsHelp.cs file and related project files to improve test consistency and accuracy. The most important changes are summarized below:

Updates to test constants and assertions:

• Changed InlineData attributes to use TestingConstants instead of Constants for better clarity and consistency.
• Updated regex patterns in assertions to match the correct output format and handle different directory separators. [1] [2]

Project file adjustments:

• Removed unnecessary Compile directive for GivenDotnetTestBuildsAndRunsHelp.cs in dotnet.Tests.csproj.

Namespace updates:

• Updated namespace usage to Microsoft.DotNet.Tools.Common for better alignment with the project structure.

Relates to #45927