Split code for the Workbox library when using the `InjectManifest` class

Currently, when one uses the [`GenerateSW`](https://developer.chrome.com/docs/workbox/modules/workbox-webpack-plugin#type-GenerateSW) class from the [`workbox-webpack-plugin`](https://developer.chrome.com/docs/workbox/modules/workbox-webpack-plugin) in their [Webpack](https://webpack.js.org) config, a separate runtime file is created for the Workbox library by default (called something like `workbox-[hash].js`). This behavior can be configured via the [`inlineWorkboxRuntime`](https://developer.chrome.com/docs/workbox/modules/workbox-webpack-plugin#property-GenerateSWConfig-inlineWorkboxRuntime) option, which has the default value of `false`.

There is no such option for the [`InjectManifest`](https://developer.chrome.com/docs/workbox/modules/workbox-webpack-plugin#type-InjectManifest) class, though. I would like to separate the Workbox runtime from my custom service worker file, too. That would allow me to cache the former (the bigger) file. Would that be possible to implement?