Add test coverage calculator and display to the test runner

[TimPurdum]

Create a way in the test runner project (Core.Test.Blazor.Shared) to check which classes, methods, and properties are tested, and show a UI that demonstrates what is tested. This could use existing nuget packages, integrations with IDE code coverage, or be in the browser like our test runner with custom UI.

[TimPurdum]

A good first step of this would be to output a list of classes that we do/don't test. This would also help us create a gissue backlog for testing.