Support for .NET 6 (#32)

* Add support for .net 6
* Update vs version
* Update test library versions
* Update nuget key
* fix .net framework versions for test discovery
* Update solution version
* Use simpler test finder

Update nuget key

Update test library versions

Update release notes

Publish new symbol format

Publish new symbol format

Switch to new project file format for tests

Switch to new project file format for tests

#21: Use base interface for EF Core 2.1/3.1 compatibility.

Update nuget key