feat: Add app.getLocaleCountryCode() method for region detection (#15035)

* Add method to get system´s user region

* Fix linter

* Remove auto types

* Improved detection for POSIX

* Change name, add specs, minor fixes

* Remove left overs

* Fix locale test

* Fix Linux test

* Coding style fixes

* Fix docs

* Add test excaption for Linux

* fix spelling

* Polishing

atom/browser/api/atom_api_app.h

@@ -182,6 +182,7 @@ class App : public AtomBrowserClient::Delegate,
 
   void SetDesktopName(const std::string& desktop_name);
   std::string GetLocale();
+  std::string GetLocaleCountryCode();
   void OnSecondInstance(const base::CommandLine::StringVector& cmd,
                         const base::FilePath& cwd);
   bool HasSingleInstanceLock() const;