Alan Agius 04f5dfe5e2 fix(@angular-devkit/build-angular): use new Webpack watch API in karma webpack plugin
In Webpack 5, the Webpack callback must be used when Webpack is running in watch mode.

Related warning
```
.(node:6565) [DEP_WEBPACK_WATCH_WITHOUT_CALLBACK] DeprecationWarning: A 'callback' argument need to be provided to the 'webpack(options, callback)' function when the 'watch' option is set. There is no way to handle the 'watch' option without a callback.
```
2021-04-20 09:27:05 -05:00
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