Simplify error messages against intersections of weak types

I spoke a bit with @sandersn about ways we can tackle the type madness issue (#14662). I noted that JSX scenarios are much more broadly applicable right now and are pretty prevalent given the sorts of type arithmetic we see a lot of in the React community. 😃

Problem: JSX optional attributes make errors too hard to read

interface FooProps {
    name: string;
    age: number;
}

class Foo extends React.Component<FooProps> {
    constructor(props: FooProps) {
        super(props)
    }
    render() {
        const {name, age} = this.props;
        return <div>I'm {name} and am {age} years old</div>;
    }
}

// Type '{ blah: number; }' is not assignable to type 'IntrinsicAttributes & IntrinsicClassAttributes<Foo> & Readonly<{ children?: ReactNode; }> & Reado...'.
//   Type '{ blah: number; }' is not assignable to type 'Readonly<FooProps>'.
//     Property 'name' is missing in type '{ blah: number; }'.
<Foo blah={10} />;

Proposal

When doing relation checks against an intersection target, if a check fails, see if relating against the same type with weak types removed would result in the same outcome. If so, use that comparison when elaborating types.

The great part is that this actually solves a broader set of problems than just JSX.

Start with the JSX reproduction in the issue and trace the type-relation checks for an intersection target with weak types. Compare the current diagnostic with the proposed comparison that removes weak types; done means the JSX error is simplified without changing the relation result, while broader affected cases remain covered.