Ensure WoltLab Suite's autoloader runs first

Ensure WoltLab Suite's autoloader runs first

While we already configured composer's autoloader with:

    "prepend-autoloader": false,

in composer.json, the laminas-zendframework-bridge registers an autoloader by
itself and prepends it.

This autoloader will not match anything more often than not and certainly
nothing that can be loaded by WoltLab Suite's autoloader, thus needlessly
burning CPU cycles.

Fix this by:

1. Explicitly prepending WoltLab Suite's autoloader in the call to
   `spl_register_autoload()`.
2. Loading composer's autoloader (and by extension the autoloader of the
   bridge) before loading core.functions.php which will load WoltLab Suite's
   autoloader.