Deprecation: #99916 - Site language "direction" setting 

See forge#99916

Description 

A language configuration defined for a site has had various settings, one of them being direction. The setting is used to add the dir attribute to the <html> tag of a frontend page in HTML format, defining the direction of the language.

However, according to https://meta.wikimedia.org/wiki/Template:List_of_language_names_ordered_by_code the list of languages that have a directionality of "right-to-left" is fixed and does not need to be configured anymore.

Since TYPO3 v12 it is not necessary to set this property in the site configuration anymore, and has been removed from the backend UI. The information is now automatically derived from the locale setting of the site configuration.

As a result, the amount of options in the user interface for integrators is reduced.

The PHP method SiteLanguage->getDirection() serves no purpose anymore and is deprecated.

Impact 

Using the PHP method will trigger a PHP deprecation notice.

An administrator can not select a value for the direction setting anymore via the TYPO3 backend. However, when saving a site configuration via the TYPO3 backend it will still keep the direction setting so no information is lost.

Affected installations 

TYPO3 installations actively accessing this property via PHP or TypoScript, and mainly related to TYPO3 installations with languages that have a "right-to-left" reading direction.

Migration 

No migration is needed as the explicit option is still evaluated. It is however not necessary in 99.99% of the use cases. If the locale of the site language in the site's config.yaml matches the natural direction of the language (Arabic and direction = rtl), the setting direction can be removed.

Any calls to SiteLanguage->getDirection() can be replaced by SiteLanguage->getLocale()->isRightToLeftLanguageDirection() ? 'rtl' : 'ltr'.

The frontend output does not set ltr in the <html> tag anymore, as this is the default for HTML documents (see https://www.w3.org/International/questions/qa-html-dir).