JS: add fs.open/openSync as writing file system calls

[erik-krogh]

And adds a Fs module similar to the NodeJSLib::Path module.

Adds support for the sink in CVE-2018-1002204

[esbena]

LGTM.

Lets update the change note to:

| Zip Slip (`js/zipslip`) | More results | This query now recognizes additional vulnerabilities. |

Super minor nit: the module name Fs is awkward to look at. Asger, will you give a 👍/👎 on that name?

[asgerf]

the module name Fs is awkward to look at. Asger, will you give a 👍/👎 on that name?

I agree. Could you rename it to NodeJSLib::FS?

When it comes to capitalization I think the Dart style guide got it exactly right, and I personally try to stick with that. In particular, two-letter acronyms are fully capitalized, so you get UIHandler instead of the ugly UiHandler, and likewise, FS instead of Fs.

[erik-krogh]

A quick smoke test came back fine