more coverlet.msbuild.tasks tests

[Bertk]

• increase source code coverage
• unit test for coverlet.msbuild.tasks
• use ILogger instead of Console.Write

[Bertk]

The updates allow to run coverlet tests code coverage (first time without errors) but the CI fails ...

dotnet test /p:CollectCoverage=true /p:CoverletOutputFormat=opencover

[Bertk]

Replaced with PR #1534