From now on all hooks will be run inside Skin.php.
Having less hooks will simplify how we construct menus.
https://www.mediawiki.org/wiki/User:Jdlrobson/Skins_for_extension_developers#Modifying_Menus
= Acceptance criteria
[] The SkinTemplateOutputPageBeforeExec has been deprecated (T60137)
[] The SkinTemplatePreventOtherActiveTabs hook is deprecated (unused)
[] The SkinTemplateTabAction hook is deprecated (unused)
[] The SkinTemplateNavigation hook is replaced with a SkinNavigation hook to operate using a Skin class rather than SkinTemplate. This hook unlike the existing hook will also run on titles that don't exist.
[] The SkinTemplateNavigation::SpecialPage is deprecated in favor of the new SkinTemplateNavigation. Callers must use `$skin->getTitle()` to check whether the page is a special page
[] The existing SkinTemplateNavigation::Universal can be replaced with a SkinTemplateNavigation::SpecialPage and SkinTemplateNavigation hook. When the new SkinNavigation hook is available we will recommend that callers use this instead.
[] SkinAddFooterLinks is promoted from SkinTemplate.php to Skin.php (it already uses the skin) and currently only lives in that class for compatibility reasons.
[] The PersonalUrls hook is replaced with SkinPersonalUrls run inside Skin.php. Hook subscribers will be given a Skin instance instead of a SkinTemplate. We migrate existing PersonalUrls hooks to the new hook before deprecating it.