Reintroducing TypeChat.Schema as a project and standalone package, with no dependency on the TypeChat project
Marking some extensions as internal unless/until they're needed outside the package, to avoid polluting intellisense for all users including these projects
Removing net60 and net70 framework targets for projects that don't need or use them (where netstandard2.0 already provides all functionality in use). Note: these can be added back at any time, if newer functionality is needed.
This change includes the following: