Use Webpack DLL feature for vendor bundle for improving build times

[swernerx]

To improve build times it seems reasonable to use the DLL feature of Webpack. This is especially interesting for development. We already have a vendor bundle handling in edge-builder. This somehow needs to be extended in a way so that the vendor bundle is created upfront, when missing, and re-used afterward.

[swernerx]

There is also a Webpack plugin automating the whole process. Unfortunately, the development stalled a few months ago. We might re-evaluate if this is helpful: https://github.com/asfktz/autodll-webpack-plugin

[fetchTe]

Good news on this front Webpack 4 support should be expected in the near future.

asfktz/autodll-webpack-plugin#105