Automate discovery of unused helper methods

We've been working on developing a tool for discovering unused helper methods that could be automated. Removing unused ("dead") code lowers the complexity of the code base and improves testing performance. It has potential to drive down bug and security reports, by reducing the surface area of each classes API, and removing the risk of "zombie code" accidentally being reactivated.

(Originally opened as a wide-ranging issue to discover dead code, we've moved that into &18110 as the majority of our discussion and work captured by this issue relates solely to the unused helper method project.)