Resolve #3422895: Document creation of new config override object if none exist
requested to merge issue/drupal-3422895:3422895-configurablelanguagemanagerinterfacegetlanguageconfigoverride-and-languageconfigfactoryoverrideinterfacegetoverride into 11.x
Closes #3422895
Modify PHPDoc of ConfigurableLanguageManagerInterface::getLanguageConfigOverride() and LanguageConfigFactoryOverrideInterface::getOverride() to document that if there is no config override for the requested language code, a new config override object is instantiated.