[5.8] Fix http kernel return docblock

[seriquynh]

The Illuminate\Foundation\Http\Kernel::handle() method has to return an Illuminate\Http\Response instance as which type it is hinted.

The Illuminate\Foundation\Http\Kernel::renderException() method also has to return the same type because it's called inside the handle block and it's result may be returned from handle on catching an exception.

[sisve]

This looks weird. The ExceptionHandler::render method is documented to return a Symfony response, so Kernel::renderException would also return a Symfony response. The Kernel contract states that the Kernel::handle should also return a Symfony response, it's just the Kernel implementation that returns a more specific one.

Perhaps it would make sense to change the Kernel's handle implementation's docblock to allow returning a Symfony response?

[GrahamCampbell]

I think the current doc is fine. Also, I swear we keep getting PRs to change this back and forward @taylorotwell?

[taylorotwell]

I'm done with these docblocks. Like 50% of all PR traffic is now docblocks.