feat: LanguageCode = string

[EdJoPaTo]

WmLanguageCode is too specific for Wikibase and only relevant on Wikidata.

This is a breaking change as WmLanguageCode and languages are gone.

closes #111

[maxlath]

I'm fine with export type LanguageCode = string but would like to keep export const wikimediaLanguageCodes, as it is arguably still useful for some projects working with Wikibase, even if mostly when working with Wikidata (I primarily have in mind inventaire, which is the project that motivated this lib in the first place ;)). Those languages being accessible in scripts/update_wikimedia_constants.ts#L32, it should be straightforward to re-include them(?)

[maxlath]

@EdJoPaTo For the needs of the review, I locally rebased on main and solved the conflicts, I can push that rebased+resolved branch here if you like.

[EdJoPaTo]

As wikimediaLanguageCodes is back now and WmLanguageCode has a deprecated export this shouldn't be a breaking change anymore if I am correct and haven't overlooked something.