Configure the projects so that they target both the netcoreapp31/netstandard20 as they currently do and add support for .NET 5.

So all our project files in the future should target both the netcoreapp31/netstandard20 and .NET 5.

• Configure project files
• Make sure all the current samples and tests work without any changes
• Create .NET 5 sample for Blazor WebAsembly (can be identical to the Blazor Server Sample)