Provides shipping country modal selection

Problem/Motivation

I have a store with several shipping and billing countries.
Users select shipping country before buy products from modal popup with the list of countries.
After that i can show prices with correct VAT.

When user starts checkout i need that shipping and billing profile don't show country select because there is only one country as available countries. the profile gets selected country and show the right address fields.

I got this but may be useful change buildPaneForm function in ShippingInformation.php class to better extend class.
line 215

    $store = $this->order->getStore();
    $available_countries = [];
    foreach ($store->get('shipping_countries') as $country_item) {
      $available_countries[] = $country_item->value;
    }

create a function getShippingCountries() so i can override the function and return available countries array.
It will great if there is an event to provides available countries so i can use it in all application.

This use case may be included as new feature in next release.

Thank you

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes