webpack-sample: include extension test example

I have difficulties with setting up extension tests when using webpack.
It looks like there was a test sample before, but now it's gone.

Would be nice if the example contains the best practice / example when webpack is in use.

In particular, I want to learn:

• How to set up the preLaunchTask for Extension Tests correctly in launch.json: Currently Extension Tests configuration is using "npm: test-compile", that invokes only "tsc -p ./". package.json points to the webpacked "./dist/extension" as the extension main. As a result, when the task starts, it's possible that the test runs the webpacked version built with a stale version of code.

• How to set breakpoints in the extension code (src/*.ts) when debugging a test using the "Extension Tests" configuration:
  Breakpoints set in the main extension source code (src/*.ts) sometimes never hit. Not sure if that's related to the fact the runTest is loading the webpacked version or whether some javascript optimization gets involved. Example to demonstrate how to make it work correctly is greatly appreciated.