Added two endpoints to TestLocalizerController for retrieving culture from Accept-Language and user cookies. Enhanced GetCulture extension to parse and return the actual culture string from cookies. Updated usings for new extension methods.
Introduced a new extension method, GetCultureByAcceptLanguage, in the WebExtensions class. This method parses the Accept-Language header from the HTTP request and returns the first valid CultureInfo, enabling detection of the user's preferred culture from browser settings.
