Enable the "navigate to test" feature in VS Test Explorer for razor-based tests

[egil]

A part of the custom xUnit RazorTestDiscoverer that is currently missing is the ability to lookup the test in a .razor file, by double clicking on the test in the VS Test Explorer (and perhaps also in VS Code and others.

To do so, all RazorTestCases must be provided with a ISourceInformation, which contains a file path to the .razor file and a line number.

It should be possible to use the System.Reflection.Metadata package to get the filename of the generated test component's .cs file, based on the type and assembly the razor test available in the test discoverer, and then from the .cs file find the .razor file and figure out the line number.

Initial attempts with the metadata API hasn't been successful though: https://github.com/egil/FindSourceFilePath

This depends on #103 PR being merged.

[egil]

The naive implementation of line finder is done. Hope for a more stable solution in the future via https://github.com/dotnet/aspnetcore/issues/21368.