Function SetKeyRoutingEventHandlerMiddleware

SetKeyRoutingEventHandlerMiddleware(
context: BlueprintContext<IBlueprint, ClassType>,
next: NextMiddleware<BlueprintContext<IBlueprint, ClassType>, IBlueprint>,
): Promise<IBlueprint>
Blueprint middleware: make the light key-router the kernel event handler.

Mirrors SetRouterEventHandlerMiddleware. Since both the full router and the light router claim stone.kernel.eventHandler, they are mutually exclusive: this throws when the full @Routing blueprint (stone.router) is also present.
Parameters
- context: BlueprintContext<IBlueprint, ClassType>
  The blueprint context.
- next: NextMiddleware<BlueprintContext<IBlueprint, ClassType>, IBlueprint>
  The next pipeline function.
Returns Promise<IBlueprint>
The updated blueprint.

Throws
When @Routing() and @KeyRouting() are used together.