Add handleFetch back in for development

[bnikom]

Library Affected:
workbox-build, workbox-sw

Is it possible to add the handleFetch option back into WorkboxSW and workbox-build? It's a convenient part of the build chain that helps separate development and production builds. I understand there's a feature in the Dev Tools application tab that easily mimics this option, but having it built into the build process is a fail-safe if a developer forgets, is unused to using the Dev Tools feature, or just doesn't totally understand how service workers work.

I'm open to discussing it, but in the previous thread (where this feature was removed)
#1002
it was mentioned that the discussion can be re-opened if people ask for it.

[jeffposnick]

At this point, especially as we move away from workbox-sw for our "recommended" developer experience, I don't think we're going to add this back.

It can, to some extent, be replicated by using process.env.NODE_ENV inside of if() statements prior to bundling your service worker.