Convert toolbar_element_info() to Element classes

PHP Traits are the worst.

(If a parent and child class both use *the same exact trait* it is considered an error)

Rerolled for now without the hook_element_info() removal in light of #2326409: Annotate render element plugins

1. +++ b/core/modules/toolbar/src/Element/Toolbar.php
   @@ -0,0 +1,105 @@
   +        // The id cannot be simply "toolbar" or it will clash with the simpletest
   

   More then 80 chars.

2. +++ b/core/modules/toolbar/src/Element/Toolbar.php
   @@ -0,0 +1,105 @@
   +    $breakpoints = \Drupal::service('breakpoint.manager')->getBreakpointsByGroup('toolbar');
   ...
   +    $items = \Drupal::moduleHandler()->invokeAll('toolbar');
   ...
   +    \Drupal::moduleHandler()->alter('toolbar', $items);
   

   I think we should inject these.

3. +++ b/core/modules/toolbar/src/Element/ToolbarItem.php
   @@ -0,0 +1,95 @@
   +   * A tray is a responsive container that wraps renderable content. Trays present
   

   more then 80 chars.

4. +++ b/core/modules/toolbar/src/Element/ToolbarItem.php
   @@ -0,0 +1,95 @@
   +    $id = drupal_html_id('toolbar-item');
   

   This is deprecated.

Thanks for the fixes.

Committed and pushed to 8.x. Thanks!