Allow specifying public path for worker files

[jimmydief]

We use Webpack's dynamic public path feature to set the URL from which we fetch our static resources at runtime. This allows us to programmatically enable/disable use of our CDN. Unfortunately, loading cross-origin workers is not allowed for security reasons so it's important that we continue to load worker files from the page origin even when the CDN is enabled.

In order to make this possible, a publicPath option could be introduced that overrides the normal Webpack dynamic/compilation public paths if specified. This option is already supported by worker-loader, mini-css-extract-plugin, and other similar tools.