Fix required prop types for classes with annotated methods.

[ethanjgoldberg]

The react/prop-types rule incorrectly considers flow type
annotations on class methods with arguments named props as
prop type declarations for the class, even though flow itself
gives them no such weight.

When a react component is defined as a class extending React.Component,
and it defines a method that takes an annotated argument named props,
then, even though flow still thinks the props have any type, the
prop-types rule will not produce 'missing in props validation' errors.

A pattern that gets used a lot in React components is as follows:

type Props = {...};
class Comp extends React.Component {
  constructor(props: Props) {
    super(props);
    // do something...
  }

  // ...
}

which makes this especially nefarious.

[ethanjgoldberg]

I've rebased this to fix the merge conflicts and bring the branch up to date -- could we get it merged this time? :)

[ljharb]

@yannickcr it'd be great to get a release out with this fix in it; any chance you'll have time soon?

[ethanjgoldberg]

@ljharb, I think this one is actually fixed by the latest flow (first change listed here) -- might be irrelevant now or possibly even wrong. I haven't tested the new flow, but I suspect this should be reverted.

[ljharb]

We need to support both versions of flow, so reverting it wouldn't work by itself