WIP: ES6 Modules

Allow for gjs scripts to use es6 import syntax:

• Import other JS modules
• Import C Modules

(optional)

• Move GIR import logic to JS

Open Questions:

How do we handle loading scripts (as opposed to modules)?

Module loading forces strict mode so we can't load old scripts as modules. We need a way to distinguishing. Options include:

• Using .jsm files (a la node)
• Requiring a command line flag like -m (a la mozjs shell)
• Autodetection of module semantics (a la typescript)

There's also the question when a module wants to import a script. I think the least janky way to do this is to require the use of the legacy imports interface for such a thing, but I'm open to suggestions.

Import resolution semantics

Do we auto-resolve import mod from "foo/bar" to foo/bar/index.js if bar is a directory. I think we should. How does name resolution work for gir imports?