Rename projects to remove "Modern"

This was a leftover from an earlier edition of the project. I had to copy some things side by side to convert from .NET Framework to .NET Core (which then became .NET 5 --> 6).

The convention is no longer necessary and is odd when someone doesn't have the history.

Start by locating the solution and project files whose names include “Modern,” then trace references to those names across the repository. Rename the projects and update every affected reference, and verify that the solution still builds.

Written by the indexing model from the issue text.