Ability to pass match params to element

[steinybot]

I'm using react-router with @loop-payments/react-router-relay which is pretty sweet but non-Relay entry points are a little ugly.

I really don't like having routing information in my components and avoid it as much as possible. It entangles the component and routing information together unnecessarily and is harder to maintain.

In v5 it was possible to do:

      <Route
        path="/users/:id"
        render={({ match }) => (
          <User id={match.params.id} />
        )}
      />
      ```
This is far more maintainable than the v6 version:

function User() {
let { id } = useParams();
// ...
}

  <Route path="/users/:id" children={<User />} />
  ```

In the v5 version the ":id" magic string is right there with the .id property. It's far easier to change. It is also possible to use this component from a different route with different parameters or at a different part of the component hierarchy where the id comes from somewhere else.

I propose allowing element to be a function. i.e.:

 element?: React.ReactNode | DataFunctionArgs<any> => React.ReactNode | null;