tags: update to latest iso-code and support more languages

Some languages have an ISO 639-2 representation but no 639-1 representation, for example where "eng" has a two-letter equivalent in "en", "enm" doesn't have one.

Discarding those languages from our static table caused functions such as gst_tag_get_language_code_iso_639_2T() or gst_tag_get_language_code_iso_639_2B() to return NULL for valid language codes such as "enm", potentially causing users of these API such as mpegtsmux to discard language code tags as invalid.