V12: Add ISO codes to make the migration from language IDs easier

[elit0451]

Details

• In relation to the concerns from Obsolete language ID related properties and methods for V13 #13753, this PR introduces IDictionaryTranslation.LanguageIsoCode and DictionaryTranslation.LanguageIsoCode and ILanguage.FallbackIsoCode and Language.FallbackIsoCode properties, to make the migration from language IDs easier;
  • The obsoletion messages related to language IDs are changed to V14 (instead of 13).

Test

• Use the following test controller and the debugger to inspect each object in dictionaryItem.Translations and allLanguages as it says in the comments in the code:

using Microsoft.AspNetCore.Mvc;
using Umbraco.Cms.Core.Services;
using Umbraco.Cms.Web.Common.Controllers;

namespace Umbraco.Cms.Web.UI;

public class TestController : UmbracoApiController
{
    private readonly ILocalizationService _localizationService;

    public TestController(ILocalizationService localizationService)
    {
        _localizationService = localizationService;
    }

    // /umbraco/api/test/test
    public IActionResult Test()
    {
        // check that each translation has a valid LanguageIsoCode now
        var dictionaryItem = _localizationService.GetDictionaryItemByKey("test");

        // check that each language has a valid FallbackIsoCode (compare with FallbackLanguageId)
        //      when FallbackLanguageId is null, FallbackIsoCode is also null
        //      when FallbackLanguageId is set, FallbackIsoCode value should correspond to the given FallbackLanguageId
        var allLanguages = _localizationService.GetAllLanguages();

        return Ok("Working");
    }
}

[nikolajlauridsen]

There's a couple of breaking changes we should get resolved first 😄

[nikolajlauridsen]

Looks good and tests good now 💪😄

Will merge when lights go green 🎉