Feature: #85900 - Pseudo Site Handling

See Issue #85900

Description

The new site handling functionality has a counterpart for usages within PHP code where no site configuration can be found, which is named "Pseudo Site", a site without configuration.

For a pseudo-site it is not possible to determine all available languages (as they are only configured in TypoScript), or the proper labels for the default language (as this is done in PageTSconfig), however, a PseudoSite or Site object (both instances of "SiteInterface") is now always attached to every Frontend or Backend request via a PSR-15 middleware.

Impact

Extension Developers can now access a site and determine the base URL / Entry Point URL for a site, or access all available languages via the SiteInterface object, instead of querying sys_domain or sys_language respectively.