Replace custom language names list with standard Intl DisplayNames API

In src/editors/data/constants/video.js, there is an object called videoTranscriptLanguages which holds a mapping from language code to language name.

This should be removed and instead we should just use the standard Intl.DisplayNames API which is built into every browser and does the same thing, without us needing to maintain the list of languages or their translations.

const languageNames = new Intl.DisplayNames(["en"], { type: "language" });
languageNames.of("pt-BR");
// Result: 'Brazilian Portuguese'

const languageNames = new Intl.DisplayNames(["pt-BR"], { type: "language" });
languageNames.of("pt-BR");
// Result: 'português (Brasil)'

It's also available in react-intl as formatDisplayName but you might as well use the native API directly.