Check for webpack

[chrisdias]

VSCE should check to see if an extension is webpack'd and if not, print out a link to the (forthcoming) documents on how to webpack an extension. this will help the ecosystem keep/make VS Code fast.

[alefragnani]

That’s a great idea 👍

I would suggest to add webpack option/configuration on Yeoman generator as well.

[joaomoreno]

/duplicate #333