Add better support for _app.js. Move types to separate module.

[parkerziegler]

Fix #36

This PR does a few things, most importantly fixing how next-urql returns pageProps when wrapping an _app.js component. We weren't handling this properly previously when running the prepass step. _app.js has a special props signature.

const App = ({ Component, pageProps }) =>

in contrast to a regular Page component, which just consumes its props directly. The extra pageProps layer is something we needed to take into account in our HoC. Moreover, we also need to ensure we use the proper ctx signature for _app.js vs. Page components, as these structures differ as well. This PR adds an isApp check inside getInitialProps such that we attach urqlClient to the correct ctx object.

In order to make a lot of this work, I loosened the types a bit by moving away from our generics. This is fine, since the HoC doesn't really care about any props coming in from the outside (it just forwards them along), and users can just specify their component's prop types in userland.

Finally, I moved our types into a separate ./types module to make them easier to read ✅

[parkerziegler]

I went for naming this AppOrPage – a much better description of what this can be!

[parkerziegler]

_app and Page components have different prop signatures, so we need to use the correct ones depending on what AppTree actually is.

[kitten]

That makes a lot of sense! Happy we can increase consistency here to smooth over the Next.js API quirks 🙌

[nghiepdev]

💯 💯 💯