Lightbulb integration and perf test in C# + C# Dev Kit

[mikadumont]

Add a lightbulb perf test to the Dev Kit suite - testPerf.yml - Repos (visualstudio.com). It would be good to cover 2 things:

1. Expand the existing open solution test to trigger lightbulb as a first invoke of lightbulb in the highly contested load timeframe
2. Add a new lightbulb test that tests it after the session settles down