WIP: types and type tests

[chriskrycho]

Fixes #38. Needs a rebase!

[mamiller93]

@chriskrycho how can I help to get this finished? I started defining the types locally to be able to use this in my own codebase.

[chriskrycho]

@mamiller93 a few steps:

1. Add the rest of the type definitions. (I don't remember which those are off the top of my head, but you can compare from the types vs. the public API.)
2. Use expect-type alongside the runtime tests to validate the expected interface. Note: prefer the .toEqualTypeOf matcher; do not use the .toMatchTypeOf. The former will blow up if we accidentally widen (e.g. to accidentally start returning any somewhere), the latter will let it pass.

That should do it. Feel free to open a PR against this PR with that set of changes! Note that I may be slower to respond, however, as I'm on vacation until Aug. 2.

[esbanarango]

🙏

[basz]

Friendly reminder this is still open... Something blocking? Would love to use TS.

[RobbieTheWagner]

Anyone interested in pushing this over the finish line?

[chriskrycho]

I'm going to push it over the finish line either in the next two weeks (if I get Ember's core types published!) or in mid-January if no one beats me to it. It's simple and easy, though, so someone should beat me to it. ;)