Add support for PHP Attributes in EntityUsageTrack plugin type

Problem/Motivation

Drupal core now supports #3252386: Use PHP attributes instead of doctrine annotations. Per https://www.drupal.org/node/3395582 , Not providing an attribute class is deprecated in Drupal 11.2 and will no longer be supported in Drupal 12.

This module should provide PHP attribute support as soon as possible so that custom implementations can begin transitioning from Annotations to Attributes.

Since the minimum compatible version of Drupal core is already 10.2, the Doctrine annotation syntax can be removed.

Entity Usage should specify a future plan for removing the Annotations classes, at which point all custom implementations must be converted to Attributes. This should be part of a new minor version release, since implementers of entity_usage plugins will need to convert existing plugins from annotation to attribute syntax.

References

• https://www.drupal.org/node/3395575
• https://github.com/palantirnet/drupal-rector/blob/main/docs/core_plugin_...
• https://www.noreiko.com/blog/big-plugin-attribute-change-over-made-easy
• https://www.drupal.org/node/3229001

Remaining tasks

1. Register the plugin Attribute class.
1. Add Attribute notation to each EntityUsageTrack plugin instance.

User interface changes

None.

API changes

Initially, PHP Attributes are supported while PHP Annotations are deprecated. The module maintainers should specify a planned date when Annotations will be removed (possibly concurrent with providing Drupal 12 compatibility?)

Data model changes

None.