Add Prefix in TestContext.AddTestAttachment for long file paths

[Meet2rohit99]

Fixes #4353.

For .NetFramework, with file path greater than 260, TestContext.AddTestAttachment was throwing attachment not found exception. As suggested prefixing "\\?\" with absolute path works fine. The issue is with .NET Framework variants but not on .NET Core3.1, .NET6, or .NET7. Therefore adding prefix only in case of .NetFramework

              string prefix = string.Empty;
  #if NETFRAMEWORK
              if (filePath.Length > 260)
                  prefix = @"\\?\";
  #endif
              if (!File.Exists($"{prefix}{filePath}"))
                  throw new FileNotFoundException("Test attachment file path could not be found.", filePath);

[Meet2rohit99]

@dotnet-policy-service agree

@dotnet-policy-service agree

[stevenaw]

Thanks for your contribution @Meet2rohit99
The changes themselves look great! Would you be able to add a test for your change too?

[Meet2rohit99]

Thanks for your contribution @Meet2rohit99 The changes themselves look great! Would you be able to add a test for your change too?

Thanks @stevenaw! Added test.

[manfred-brands]

See comments in PR.

[manfred-brands]

Thanks. Looking good now. Builds are all green.

[stevenaw]

Thanks for your contribution @Meet2rohit99 ! This looks good to me too