Use cache-busting Webpack chunk names in development (#2920)

#2864 introduced Webpack bundle
splitting. While the chunk names are based on a rolling integer number
in production, they are deterministically computed based on the filename
in development. Browser caching causes this to be annoying in
development. This PR changes the naming scheme to instead depend on the
content hash, eliminating the issue.

Author: williamjallen

webpack.mix.js

@@ -112,6 +112,9 @@ mix.webpackConfig({
   stats: {
     children: true,
   },
+  output: {
+    chunkFilename: 'assets/js/[contenthash].js',
+  },
   optimization: {
     runtimeChunk: false,
   },