`VisibleTranslationState` was a wrapper around a `TranslationState` that was
meant to public API consumers outside of this crate. However, the internal
`TranslationState` and all its methods were still publicly exposed! This commit
simplifies and remedies the situation by combining them into a single
`TranslationState` type. Most of its methods are only `pub(crate)` now, not
visible to the entire world. The only methods that are `pub` are the ones that
`VisibleTranslationState` exposed.
* the target-lexicon crate no longer has or needs the std feature
in cargo, so we can delete all default-features=false, any mentions
of its std feature, and the nostd configs in many lib.rs files
* the representation of arm architectures has changed, so some case
statements needed refactoring
