Issue #2100073 by dawehner: Convert local_actions() to the new local action plugins.

core/core.services.yml

core/includes/menu.inc

core/lib/Drupal/Core/Controller/DialogController.php

core/modules/aggregator/aggregator.local_actions.yml

core/modules/aggregator/aggregator.module

core/modules/contact/contact.local_actions.yml

core/modules/contact/contact.module

core/modules/contact/contact.routing.yml

core/modules/menu/menu.local_actions.yml

core/modules/menu/menu.module

core/modules/node/node.local_actions.yml

core/modules/node/node.module

core/modules/path/path.local_actions.yml

core/modules/path/path.module

core/modules/picture/picture.local_actions.yml

core/modules/picture/picture.module

core/modules/shortcut/shortcut.local_actions.yml

core/modules/shortcut/shortcut.module

...system/lib/Drupal/system/Plugin/Block/SystemHelpBlock.php

...odules/system/lib/Drupal/system/Tests/Ajax/DialogTest.php