Improve TypeScript experience when dependencies are missing.

[trusktr]

I was in a project, and forgot that I deleted node_modules (or forgot to npm install), and in this case I was seeing any all over the place, and was jumping myself to conclusions that something was wrong with TypeScript or VS Code.

It could be helpful if VS Code could suggest something like

Did you forget to install dependencies? Perhaps you should run npm install?

or similar.

[mjbvz]

@trusktr Were you writing JavaScript or TypeScript code when you hit this?

---

In terms of precedent for this suggestion, we do have a warning about installing @types packages:

[trusktr]

I was writing TS. That message could indeed be helpful. Another case could be if node_modules is simply missing, it could suggest installing all project dependencies with npm install.