Rewrite module to use default field storage

Problem/Motivation

The biggest part of the issues this module has are caused by its custom field storage implementation. This also adds a lot of unnecessary complexity to the module. It's reinventing the wheel, since Drupal has a whole field storage system built in that automatically deals with things like translations and revisions.

Proposed resolution

Rewrite the module to stop using the custom storage service. Instead, make the caption a standard field property whose storage is handled like any other field property in Drupal.

To address these issues, the module should be refactored to eliminate the custom storage service and instead leverage Drupal's default field storage system. This involves redefining the caption as a standard field property, allowing Drupal to handle its storage, translations, and revisions natively. By doing so, the module will:

1. Simplify the codebase: Remove the custom storage implementation and rely on Drupal's proven field storage mechanisms.
2. Improve maintainability: Reduce the risk of bugs and inconsistencies by using core functionality.
3. Enhance compatibility: Ensure seamless integration with other Drupal features, such as translations and revisions, without additional custom logic.
4. Follow best practices: Align with Drupal's architecture by utilizing its built-in field storage system.

Implementation Steps

1. Remove Custom Storage Service:
   • Delete the custom storage service and related classes.
   • Ensure all dependencies on the custom storage are removed.
2. Define Caption as a Field Property:
   • Modify the field type plugin to define the caption as a standard field property.
   • Update the schema and property definitions to reflect this change.
3. Update Widget and Formatter:
   • Adjust the field widget to handle the caption property as part of the default field storage.
   • Update the field formatter to display the caption property correctly.
4. Migrate Existing Data:
   • Provide an update hook or migration path to transfer existing caption data from the custom storage to the default field storage.
5. Test Thoroughly:
   • Ensure the changes work seamlessly with translations, revisions, and other Drupal features.
   • Verify that existing data is preserved and displayed correctly after the migration.

Remaining tasks

Provide an upgrade path.