pure-component: support Type Annotations & Class Properties

[danharper]

I was going to split this into a few PRs, but they're kinda related.

Firstly, it now treats any Component with a ClassProperty which isn't props as being impure.

Secondly, it retains any static ClassPropertys.

Finally, it retains props type annotations when transforming to a function.

I haven't used jscodeshift before, so happy to make any changes if there's a cleaner way of accomplishing it :)

// input
class PureWithTypes extends React.Component {
  props: { foo: string };
  render() {
    return <div className={this.props.foo} />;
  }
}

// output
const PureWithTypes = (props: { foo: string }) => {
  return <div className={props.foo} />;
}

[danharper]

Oh, this completely errors when running on my own project.. I guess the default parser of jscodeshift is Babylon, but not in the tests?

Edit: the Babylon errors might just be an existing issue, actually (#78).

[cpojer]

@keyanzhang can you take a look at this one? :)

[keyz]

Thanks @danharper, the code looks solid. Note: I manually restarted the build on travis to double check; all the errors are from #88 and not pure-component, so this is good to merge!

[danharper]

👍 thanks