Fix order of negotiation methods in subscriber

Problem/Motivation

In #3054850 we removed the sorting by weight, which, although correct, still left the order of the configured negotiators not work correctly.

When this module is calling

$this->languageNegotiator->getNegotiationMethods(LanguageInterface::TYPE_INTERFACE);

The plugins are returned in an unexpected order. The reason is that LanguageNegotiator::getNegotiationMethods() first gets all the plugin definitions (unsorted) and then runs an array_intersect_key with the the ones configured and ordered in the UI. So the order in the UI is no longer kept (the plugin definition order wins). It may work elsewhere for core, but in the case of this module, which loops through these and exits if it encounters the selection page plugin first, other negotiation methods which are configured in the UI to come BEFORE it no longer have a chance.

Steps to reproduce

Add a language negotiation method that gets loaded AFTER the language selection page when calling getDefinitions() on the negotiator plugin manager.