this makes translation usage much more statically analysable.
The only places this isn't used are:
- places that prefix translations with colours (those are still a problem)
- places where server/client translations don't match (e.g. gameMode.changed accepts different parameters in vanilla than in PM)
TextContainer provided zero real value as a base of TranslationContainer, given that it required its own logic to be handled wherever accepted. As such, it's no better than a simple string.
Removing it also allows fixing an ambiguity when embedding translations inside other translations, allowing it to be made immutable.
