Refactor the AccountHeaderBlock

Problem

The current AccountHeaderBlock uses a very specific and large twig file to render the various cases that occur in the account header block. A single extension hook has been made to allow adding some menu items but it's otherwise not very flexible.

Solution

Rewrite all the components in the block in such a way that they use standard Drupal render arrays. For the icons on desktop with their submenu's we create an AccountHeaderElement render element that provides some shortcuts to the developer and keeps code DRY.

Two info hooks and alter hooks are then implemented that gather up all the AccountHeaderElements as well as all the links for the profile AccountHeaderElement. We deprecate the previously created alter hook as its format is ill-defined for the new structure.

We also allow both sets of items to be sorted using weights so that the order in which hooks are called doesn't matter and sites can easily re-order them if they so choose.

Possible follow-ups

It's pretty easy to figure out which menu items exist now so it is possible in theory to create a UI for Site Managers that allows them to rearrange the order of all the items. The ordering could then be applied in an alter hook that reads the configuration.

Target version

This should land in a MAJOR Open Social update as it removes some template files.

Release Notes

The AccountHeaderBlock has been rewritten to provide more flexibility. Various hooks to alter it's behaviour have been introduced and documented in social_user.api.php. The previous hook to extend the user menu has been deprecated and will be removed in a future version.