Consider adding Roslyn component multi-targeting to templates

[Youssef1313]

It would be very useful if the default templates have the enhanced analyzers/dotnet directory layout that allows multi-targeting roslyn components. See dotnet/sdk#20793

[Youssef1313]

YairHalberstadt/stronginject@40c2721 for an example where this was done.

[sharwell]

This should be implemented such that the generated package project automatically places assemblies into the correct version folder based on the references present in the project. For example, this means a user who only changes the Version value of a project reference from 4.0.1 to 4.1.0 will see the assemblies move in the package from roslyn4.0 to roslyn4.1.