Fix Csc task usage in the FileTrackerTests.cs

[AR-May]

Some of the (currently skipped) tests in the FileTrackerTests.cs use Microsoft.CodeAnalysis.BuildTasks.Csc task from Microsoft.CodeAnalysis.Build.Tasks package. This nuget package was discontinued. We would need to reconsider this type usage if/when we are going to enable the tests back. There are several options:

1. Replace Csc usage with some mock class. We probably do not need to really generate executables during tests.
2. Or consider using Csc task from Microsoft.Net.Compilers.Toolset or maybe Microsoft.Net.Compilers, see Replacement for Microsoft.CodeAnalysis.Build.Tasks package roslyn#78956

[AR-May]

In #11877 I removed the Microsoft.CodeAnalysis.Build.Task package and hid the Csc usage behind ifdef - as a temporary measure so that we can run some of the tests in the file but not compile some of the tests.