Properly serialize ignoreURLParametersMatching RegExps

[jeffposnick]

R: @tropicadri
CC: @ognjenjevremovic

Fixes #2796

This resolves an issue with #2763 that I overlooked in my review: the ignoreURLParametersMatching RegExps were serialized to the config file as strings, which makes them invalid when they're read back and used.

This PR switches the serialization to use stringify-object (which we use elsewhere, in workbox-build) and updates the tests to ensure that RegExps are handled as expected.

[ognjenjevremovic]

@jeffposnick I apologize for the issue. I must admit I have overlooked this myself when making the PR.

When testing the changes locally (besides running the suite of unit tests), I have checked the output of the workbox wizard command and inspected the generated workbox-config.js and the value of ignoreURLParametersMatching.
However, I didn't try generating the service worker (by running workbox generateSW) which would've raised the red flags for having invalid value types inside of the generated array.

Good to see you have the fix ready 🚀 .
I apologize for any inconvenience this might have caused 🙂 .