As a developer I want the JSX support in N4JS to not ignore the properties of JSX elements/fragments

[mor-n4]

Currently, the JSX support in the N4JS compiler is producing raw types as the types of JSX elements. This is a problem because raw types are checked only partially and should therefore be used only in rare special cases.

For example:

import * as React from "react";

interface ~FooProps extends React.ComponentProps {
	public fooProp?: string;
}
interface ~OtherProps extends React.ComponentProps {
	public otherProp: string;
}

function Foo(props: FooProps): React.Element<?> {
	return null;
}

let fooTag = <Foo/>;

// XPECT FIXME errors --> "Element<FooProps> is not a subtype of Element<OtherProps>" at "fooTag"
let elem: React.Element<OtherProps> = fooTag; // this assignment should not be allowed!!

The type of fooTag will be Element (i.e. a raw type not providing a type argument for Element's type parameter), leading to the problem that the assignment in the last line is allowed. Instead, the type of fooTag should be at least Element<?>, or better Element<MyProps>.

The problem, however, is that this fix will break client code because it leads to stronger type checking.