[New Rule] Check propTypes are static

[pke]

You get this runtime warning:

warning: propTypes was defined as an instance property on MyComponent. Use a static property to define propTypes instead.

when you forget to make the propTypes static like this:

class MyComponent extends React.PureComponent {
  propTypes = {
    text: PropTypes.string,
  }
}

The new rule could detect non-static propTypes inside class definitions and report them by default as warning.

[ljharb]

This seems like something no-typos should be handling.

[ljharb]

Indeed, no-typos already handled this over a year before this was filed (see #1209)