refactor(LanguageIdentifier): Derive PartialOrd and Ord for LanguageIdentifier.

[JosiahBull]

Add Derive PartialOrd and Ord on the LanguageIdentifier type. Based on previous PRs it seems reasonably acceptable to add this implementation.

Happy to add this to other objects or make other changes if required. :)

[CLAassistant]

All committers have signed the CLA.

[Manishearth]

I believe this is a deliberate omission since there are multiple valid ways to compare these types (see: strict_cmp) and we don't want this to be a footgun.

cc @sffc @zbraniecki

[sffc]

See discussion in #1215.

Since ICU4X 1.5, we have a total_cmp function on these types that can be used to make a thin wrapper that implements PartialOrd/Ord for use in a BTreeMap.

[JosiahBull]

I appreciate the link to the previous discussion, thanks for being so polite!

Apologies for missing the previous PR removing this functionality in my initial search. 😅

[sffc]

Thanks for discovering that we lack documentation about this! Adding it here: #5296