[UX] Admin Bar: Add a single, centralized point of entry for adding content, files, user accounts etc.

This feature request is inspired by New “content creation” menu proposal and Add "Add" item to toolbar.

Adding content is a critical function in Drupal. While we have added a tools block and a default shortcut for this EVERY OTHER MAJOR CMS puts an add or create content link in the MAIN toolbar. This is marked critical because it is a critical usability problem in Drupal that a new user has to hunt around just to find where to do the most fundamental thing that a CMS does; create content.

Content can not only be nodes, but also media items or custom entities

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The top level admin sections result in a disjointed experience for people with primarily content creation/management focused permissions. Access to items that for these users are similar tools is spread out across multiple admin sections.

We* propose to introduce a content editor menu that brings these creation/management tasks together for easier access.