[Backport] Make State/Province required field in checkout view based on settings

[Igloczek]

It's the backport of changes present on develop branch, to fix issues described in #9077 also on 2.1.x.

Related commits and issues:

• 1b4ba9f
• 4f2fa65
• State/Province field doesn't show as required on the add new address page. #5279
• Customer country list not correct #2946

[orlangur]

Will this cover #10897 case?

[Igloczek]

@orlangur Yup, it will cover this case too.

[vrann]

@Igloczek thank you for the backport!
We notice one issue which still has to be resolved: when the State/Province is a required field, it is validated on PHP side, but the frontend does not display it as a required for the countries other than USA (i.e. India).

This is how it looks like on 2.1 after the fix:

This is how it looks like on develop

[Igloczek]

To be completely honest with you, I'm afraid that it has to be merged in the current state or rejected, because I don't have time to investigate, especially while we have 2.2 up and backport isn't a crucial thing, because users can just make an upgrade.

[ishakhsuvarov]

@Igloczek I am closing this now per your comment.
Please reopen if you feel like continuing with this one in the future.