File extension metric for each function in a function app

In V2, on the analytics side, we track metrics by language stack. There's no good metric right now for us to tell what language a specific function is though - ideally, we'd like to be able to disambiguate between TypeScript and JavaScript, for instance. Another example is .NET precompiled vs CSX. It would be interesting to see how many customers are using scala on the java worker, for instance. Any metric that emits file extensions detected for a given function would be helpful.

The issue names no file, test, or entry point, so first trace the V2 analytics metric emission path and how the host identifies each function's language stack. Confirm how TypeScript versus JavaScript, .NET precompiled versus CSX, and Scala on the Java worker are represented, then verify that a per-function file-extension metric is emitted and distinguishes those cases.

Written by the indexing model from the issue text.