[w3c/payment-request] Move PaymentAddress string defaults to AddressInit (#853)

Right now, we do a lot of "set |address| [[slot]] to the empty string". We should just move all that  prose logic to `AddressInit` by setting each member to default to `""` and `= []` for any sequence type. 

This shouldn't have any impact on developers, as the behavior we get is identical. However, it does significantly simplify implementation (as the binding layer can handle all of the above).   

-- 
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/w3c/payment-request/issues/853