Update wcs_copy_order_address() to use modern APIs for setting address fields

[james-allan]

Fixes #227

Description

While testing #226 I discovered that the billing and presumably the shipping address indexes weren't being saved correctly on checkout.

This issue happens because of the wcs_copy_order_address() function which uses a legacy function (set_address()) to copy the address data.

That function sets the address data directly into post meta. Because of that, when the subscription is eventually saved, the address field updates aren't updated here (since there is nothing changed) which causes the indexes to not be updated.

This PR replaces the set_address() functions with the respective set_shipping_address() and set_billing_address().

How to test this PR

1. Purchase a subscription on the refactor-create-subscription branch.
   • no HPOS setup is required. Just using the wp post architecture is fine.
2. In the database look at the subscription and notice the billing address index is incomplete.
   • On trunk the billing index will be incomplete (only include the email).
   • On this branch the index field will be complete.

^ trunk 👎

^ this branch. 👍

Product impact

• Added changelog entry (or does not apply)
• Will this PR affect WooCommerce Subscriptions? yes/no/tbc, add issue ref
• Will this PR affect WooCommerce Payments? yes/no/tbc, add issue ref

[mattallan]

I've just added a changelog for this one @james-allan. Feel free to change it :)

[mattallan]

I've confirmed the issue on refactor-create-subscription where creating a subscription resulted in no _shipping_address_index data being saved to the DB and only my WP account email was present in _billing_address_index (not the billing email set on checkout):

3495	27	_billing_address_index	         matt.d.a@live.com 
3496	27	_shipping_address_index	         

I've confirmed the problem is fixed on this branch:

3596	29	_billing_address_index	Matt Allan  959 Market Street  San Francisco CA 94013 US matt@example.com (555) 555-5555
3597	29	_shipping_address_index	Matt Allan  959 Market Street  San Francisco CA 94013 US 

LGTM