Add euro format

[bcolloran]

continuing the work started by @Fredehagelund92 in PR #3748

[bcolloran]

@ericpgreen2 -- note that this has been entirely disabled for months. I've commented out individual cases that are not working exactly as desired (though they are small edge cases that have not been bothersome in practice), but I reckon it's better to have most of the cases running and these ones commented out with FIXME than to turn off the whole file

[bcolloran]

@ericpgreen2 This PR adds a currency_eur format preset, and does some amount of the cleanup we talked about the other day without going too deep -- I can revisit if there are product needs that would point us in that direction.

[ericpgreen2]

Nice, thanks @Fredehagelund92 for getting this started, and thanks @bcolloran for getting it over-the-line!

As @bcolloran and I discussed, this is a short-path to add the Euro. When adding many more currencies, we should think about a more scalable strategy/syntax.