Telemetry should include whether file-based apps or projects are being used

[RikkiGibson]

We want to know how often C# extension users are using file-based apps.

The telemetry, produced during design time build, should include a few bits of info:

• are we restoring for an ordinary project or for a file based app?
• has any solution been selected?
• has project initialization completed previously?
  • If a solution is selected but project initialization is not completed, it often means we are treating the file as a file-based app simply because its real project is not loaded yet.
• is this a "rich misc files" case or a "true file-based app" case?
  • This refers to the heuristic that if no #: directives are present, and no top-level statements are being used, then use the "rich misc files" experience which offers completions and syntax diagnostics, but not semantic diagnostics.

@DamianEdwards for visibility