Add state/county field to addresses

[jacksleight]

This PR adds state/county support to the shipping and billing addresses.

Just like the zip/postal code this will allow a field named *_state (US) or *_county (UK). As SC defaults to *_zip_code for zip/postal code this mirrors that convention by defaulting to *_state.

I've also updated the PayPal gateway as the shipping address PayPal provides contains values for both city and state:

admin_area_2
A city, town, or village. Smaller than admin_area_level_1.

admin_area_1
The highest level sub-division in a country, which is usually a province, state, or ISO-3166-2 subdivision. Format for postal delivery. For example, CA and not California. Value, by country, is:
UK. A county.
US. A state.

https://developer.paypal.com/docs/api/orders/v2/

In most places SC uses the US named fields by default, but there are a couple of places where the UK named fields are used. I've mirrored these because I wanted to be consistent with the conventions already in place in SC, but I'm not sure if any of this needs to be tidied up for consistency?

1. The order blueprint has UK named fields called *_county
   • This is because it already has *_postal_code fields, not *_zip_code fields
2. The shipping docs page has a US named field called *_state but the placeholder is County
   • This is because it already has a *_zip_code field with a placeholder of Postal Code, not Zip Code
3. The PP gateway sets a UK named field called *_county
   • This is because it already sets a *_postal_code field, not *_zip_code
   • I dont know if this is a problem or not, does that mean if you're using *_zip_code and *_state they wont be updated from the PP data?

[duncanmcclean]

Thanks for this!

However, I've actually already built this (but called regions instead) in v2.4, along with updated tax features.

I'm fine with introducing this in v2.3 but we'd need call it region instead of county/state.

[jacksleight]

Ah no problem, I have updated it to region. Thanks for adding it to 2.3, it's something my client just highlighted as he would like county fields added to his site.

[duncanmcclean]

Thanks! I'll review this properly tomorrow evening!

[duncanmcclean]

Released in v2.3.47