Make use of AssetInfo in webpack build

[jeffposnick]

R: @Snugug @housseindjirdeh @philipwalton

Fixes #2221, fixes #2672

Some small changes to the workbox-webpack-plugin to take proper advantage of webpack's AssetInfo capabilities.

When we create an asset via GenerateSW and we know that it's already been compressed, we now set minimized: true.

When we read assets from the build to generate our precache manifest, if any assets have immutable: true, that's a clear sign that we don't need to generate hashes for them, so we can return null for the revision parameter. The JSDoc for dontCacheBustURLsMatching has also been updated to reflect this.

[Snugug]

This LGTM from the comments from other webpack threads, but could probably use a LGTM from someone who knows webpack 6 better than I do.