Make dotnet test logger a list of strings

[totollygeek]

According to the docs:

-l|--logger <LOGGER>

Specifies a logger for test results. 
Unlike MSBuild, dotnet test doesn't accept abbreviations: instead of -l "console;v=d" use -l "console;verbosity=detailed".
Specify the parameter multiple times to enable multiple loggers.

Which means that dotnet test supports multiple --logger arguments. This is why I want to make it List<string>.

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