Allow an interface in the JSX namespace to specify the element class type

We're writing a non-react library that uses TS's JSX support with custom interfaces defined in the JSX namespace. Unless we are very much mistaken (The documentation seems a little out-of-date in this area? Most of our current understanding comes from reading through issues on here, we may have missed something.) it seems that while ElementClass can be used to define the type of the element instance type there is no interface to limit the members of the element class type.

We have a custom component base-class and an equivalent to React's createElement function. Our createElement function needs to be able to create instances of the component classes. To be able to do this in a type-safe manner, we need to be able to specify an interface for the element class type that can require a specific constructor signature.

This feels like an oversight in the current implementation TBH. With React itself it's even possible to create components with incompatible constructors that would fail at runtime.

Beginne mit der Untersuchung der Unterstützung von TypeScript für den JSX-Namespace, insbesondere von ElementClass und dem im Issue beschriebenen benutzerdefinierten createElement-Szenario. Ermittle, wie ein Interface für den Elementklassentyp eine Konstruktoranforderung ausdrücken sollte. Die Aufgabe gilt als erledigt, wenn die JSX-Typprüfung diese Anforderung für benutzerdefinierte Komponenten durchsetzen kann, ohne das bestehende JSX-Verhalten zu beeinträchtigen.