JS: Adds basic support for webpack-dev-server and importing from neighbouring packages.

[erik-krogh]

Gets a TP for CVE-2018-6342

Does 2 things, and I'm somewhat unsure about both.

1. Recognizes route-handlers from webpack-dev-server.

Example:

const webpackDevServer = require('webpack-dev-server');
new webpackDevServer(.., {
  before: function (app) {
    app.use(someRouteHandler());
  }
});

2. Adds very basic support for importing from other packages.
   It is essentially very basic non-TypeScript monorepo support.

The resolveNeighbourPackage predicate is outside Import class because I got join-order issues otherwise. (Same reason for pragma[noinline]).

TODO:

• tests
• change note
• evaluation

[asgerf]

Cool! Nice and simple.

The import resolution is indeed something I wanted to handle via the monorepo support I've been working on, but given the simplicity of this solution I see no harm in landing that first.

[asgerf]

Hm, an unfortunate breaking change. Would it make sense to add a case in isRouter instead of this change? That's also how we incorporate type information in here.

[erik-krogh]

A performance evaluation came back, and it doesn't look too good.

But, the performance penalty comes from resolving extra imports. For example: azure-sdk-for-node has 3613 new resolved imports.
The rest doesn't seem to affect performance.
I think @asgerf should make the call whether we continue with this or not.

(The rebase below didn't change anything, it just added tests and a change-note).

[asgerf]

I think we should go ahead with this. The performance cost is unfortunate but not really the fault of this PR. Resolving imports is definitely the right thing to do.