Add @see to all plugins for the referenced plugin annotation types.

Problem/Motivation

In

modules/examples/content_entity_example/src/Entity/Contact.php

The following namespaces are not imported:

use Drupal\Core\Annotation\Translation;
use Drupal\Core\Entity\Annotation\ContentEntityType;

These namespaces belong to the @ContentEntityType and @Translation annotations.

This leads to confusion over where these annotation types come from, and make it difficult for IDEs to provide a way to look them up.

Proposed resolution

Make sure that all plugins in the Examples project have @see annotations for all annotation types used.

Add @see which links to https://plugins.jetbrains.com/plugin/7487-drupal-symfony-bridge so that people can learn to install a PHPStorm solution if they're using that IDE.

Remaining tasks

User interface changes

API changes

Data model changes