extensions: improve bundling of extensions

[vince-fugnitto]

Description

We can likely improve the loading and running of builtin extensions if we include a bundling strategy such as webpack.
Recently, vscode extensions added support to webpack extensions to reduce the overall size of extensions and doing so may improve the overall performance of all applications that make use of builtin extensions under open-vsx:

• https://code.visualstudio.com/api/working-with-extensions/bundling-extension

[vince-fugnitto]

It's possible this is already the case looking at the logs:

Ex:

[19:21:21] 
Starting bundle-extensions-build ...

[19:22:50] Bundled extension: git-ui/extension.webpack.config.js...

I'm having difficulties building the repo (master) at the moment however.