Feat/users/994 one language call to rule them all

[sonwit]

Get the user's selected language from the cookie instead of the user profile.

Description

• Rename "ProfileHelper" to "LanguageHelper."
• Stop getting the language from the user profile if not necessary.
• Continue getting the language from "altinnPersistentContext" in HomeController, and from the Profile if it doesn't exist; otherwise, use the cookie from the frontend.
• Rename the "i18next" cookie to "selectedLanguage" and use this in the frontend for loading the language.
• Simplify the mapping of languages between standards.

Related Issue(s)

• One language call to rule them all #994

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)
• All tests run green

Documentation

• User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)

[allinox]

This looks great! 😄
I like what you've done with the LanguageHelper - so useful!
Thanks for fixing up in the language stuff. It's way more robust now!

There are a few sonarcloud warnings I see have popped up in github telling us to use List.Find instead of IEnumerable.FirstOrDefault which you can consider changing if you have the time, but it's nothing major so not super important to do right this second I think.

[sonarqubecloud]

Quality Gate failed

Failed conditions
64.29% Condition Coverage on New Code (required ≥ 65%)

See analysis details on SonarCloud