Add support for per-address-format default values

commerceguys/addressing v2.2.0 will ship with support for per-address-format default values, currently defined only for Singapore.

See:
https://github.com/commerceguys/addressing/issues/209
https://github.com/commerceguys/addressing/issues/206

Once there is a v2.2.0 release and Address is updated to depend on it, we should start using $addressFormat->getDefaultValues() in the form element (in absence of an explicitly-provided #default_value, of course).