Feature: add state_label and states keys to give_get_states ajax function

[jonwaldstein]

Related: impress-org/givewp-next-gen#204

Description

This adds state_label and states to the give_get_states() ajax function for use in the new BillingAddress block from this PR.

Affects

Technically the give_get_states() but is only adding new keys, not modifying existing functionality.

Visuals

N/A

Testing Instructions

• state_label should return the state label based on the country
• states should return an array of states based on the country

Pre-review Checklist

• Acceptance criteria satisfied and marked in related issue
• Relevant @unreleased tags included in DocBlocks
• Includes unit tests
• Reviewed by the designer (if follows a design)
• Self Review of code and UX completed

[jonwaldstein]

@glaubersilva this is ready for review.

[glaubersilva]

@jonwaldstein Looks good to me! Do you think we need to send it to QA? As this does not change any previous values on the response, I believe would be ok just to merge it, but let me know your thoughts.

[jonwaldstein]

@glaubersilva thanks, yeah I'll sent it to QA just to be safe.

[rickalday]

Passed manual QA tests