Creata a ConfigOverrideLanguageCacheContext and use it in LanguageConfigFactoryOverride

Problem/Motivation

Config override language is in the general case different from interface language, but lacks cache context.

From #3446084-26: EntityTypeBundleInfo static caching is not language aware → :

> ::getConfigOverrideLanguage() always calls ::getCurrentLanguage() with no arguments, which always returns the current interface language

@catch: Yes, i used to belive this too, but it's a myth.

One thing is the difference between language negotiation and LanguageRequestSubscriber, and in the meantime a lot can happen (we can change this by making interface language negotiation setting ConfigLanguage instantly, but the current way of working might have reasons, and a change might have unforseeable consequences).

It's also that there are a lot of places where ConfigLanguage is **intentionally** changed. Look e.g. at ConfigurableLanguageManager::getNativeLanguages. It changes ConfigOverrideLanguage to retrieve the respective translations. And there are a handful of other places that do it like this.

In a well designed API, there would be sth like Config::get($name, $language) (TODO: add issue). But there is not, and so messing w/ global config language is the only way of getting the result.

And yes, this means essentially that there **should** be a ConfigOverrideLanguageCacheContext, and not having and using one is a design flaw. And indeed, in TranslationBliss module we maintain this cache context for exactly this reason. (TODO: Add issue.)

And yes, you are right, a proper memory cache (do we need variation cache?) would be the "proper" thing and (TODO:) i can add a followup for this.

Proposed resolution

- Creata a ConfigOverrideLanguageCacheContext (copy it from TranslationBliss module)
- use it in LanguageConfigFactoryOverride.

Remaining tasks

Do it, write tests, review commit.

User interface changes

None.

Introduced terminology

None.

API changes

None.

Data model changes

None.

Release notes snippet

New language_config cache context.