Add `intl/flag-AA` set from fd.o spec

[wpkelso]

According to the fd.o spec, International/flag-AA, where AA is an ISO 3166 country-code, is an expected group of icons in a compliant set

[danirabbit]

This seems like maybe it would be better to propose to be deprecated from the spec. I'm not sure what the expected use is for this but it seems like hyper specific to certain system applications

[wpkelso]

I could see it being used as a shorthand in a locale picker for something like a translation application, but I agree that even then its pretty limited. Most applications I can think of off the top of my head are pretty contrived, and most locale/language related stuff is probably handled automatically with sys locale/lang. Just noticed it was missing when going through the spec earlier 😃