Enable code analysis with roslyn analyzers

[balanikas]

Adding and enabling analyzers in the foundation solution produces warnings and recommendation that increase awareness of code issues and therefore code quality.

Add these 2 analyzers:
https://www.nuget.org/packages/Microsoft.CodeAnalysis.FxCopAnalyzers (strongly recommended) which is a collection of recommended analyzers by Microsoft.
https://www.nuget.org/packages/microsoft.visualstudio.threading.analyzers (secondary but useful) which suggests some threading related good practices.

The severity of issues in both packages can be configured but i recommend that initially the severity level is set to informational or warning, to not be obtrusive.

Add them either per project as needed, or via global configuration (i.e. analyzers.props)

[davidknipe]

I second the use on analysers. We should also add this analyser to add some Episerver best practices: https://world.episerver.com/blogs/mads-storm-hansen/dates/2019/11/introducing-code-analyzers-for-episerver/

[krompaco]

This might be a harder sell but Install-Package StyleCop.Analyzers would help as well.