CoreResGen task fails on various *Test projects

[tmeschter]

After working around/fixing other issues (#23190, #23191, dotnet/sdk#1748, etc.) we then run into errors in the CoreResGen task of CodeAnalysisTest.csproj, CSharpCommandLineTest.csproj, BasicCommandListTest.vbproj, and others. For example:

D:\Projects\Roslyn\Open\Binaries\Obj\CodeAnalysisTest\Debug\CodeAnalysisTest.xlf\Resources.cs.resx(124,5): error MSB3103: Invalid Resx file. Could not find a part of the path 'D:\Projects\Roslyn\Open\Binaries\Obj\CodeAnalysisTest\Debug\CodeAnalysisTest.xlf\Resources\default.win32manifest'. Line 124, position 5. [D:\Projects\Roslyn\Open\src\Compilers\Core\CodeAnalysisTest\CodeAnalysisTest.csproj]
D:\Projects\Roslyn\Open\Binaries\Obj\CodeAnalysisTest\Debug\CodeAnalysisTest.xlf\Resources.de.resx(124,5): error MSB3103: Invalid Resx file. Could not find a part of the path 'D:\Projects\Roslyn\Open\Binaries\Obj\CodeAnalysisTest\Debug\CodeAnalysisTest.xlf\Resources\default.win32manifest'. Line 124, position 5. [D:\Projects\Roslyn\Open\src\Compilers\Core\CodeAnalysisTest\CodeAnalysisTest.csproj]
D:\Projects\Roslyn\Open\Binaries\Obj\CodeAnalysisTest\Debug\CodeAnalysisTest.xlf\Resources.es.resx(124,5): error MSB3103: Invalid Resx file. Could not find a part of the path 'D:\Projects\Roslyn\Open\Binaries\Obj\CodeAnalysisTest\Debug\CodeAnalysisTest.xlf\Resources\default.win32manifest'. Line 124, position 5. [D:\Projects\Roslyn\Open\src\Compilers\Core\CodeAnalysisTest\CodeAnalysisTest.csproj]
...

It is not immediately clear what is going on, but my first thought is that we shouldn't be generating .xlf files for these projects at all (that is, we shouldn't be going down any part of the localization pipeline for them).

[tmeschter]

I'm planning on dealing with this by simply disabling XliffTasks for any project that doesn't produce shipping bits (e.g. <NonShipping>true</NonShipping>).