Update plugin generators to use PHP attributes

[Chi-teck]

Drupal now supports plugin discovery through PHP attributes.
https://www.drupal.org/project/drupal/issues/3252386

DCG generators needs to be updated to support this feature.

The main question is how implement this without breaking compatibility with Drupal 10.1.

Option 1
Add CLI option or question to each plugin generator to ask a user explicitely whether the plugin should use attributes instead of annotations.

Downside: A lot of work. Each plugin template will have if statements to support both types of discovery. Testing double implementation would be a nightmare.

Option 2
Use PHP attributes by default and convert them into annotations magically using AssetPreProcess event if Drupal version is below 10.2.

Downside: Testing is still hard.

Option 3
Release new DCG version (3.4) that only supports Drupal 10.2 and above.
Keep DCG 3.3 as LTS release till Drupal 10.1 is EOL.

Option 4
Do nothing. Just wait for Drupal 10.1 EOL (June, 2024) before starting work on this.

[andypost]

I think you need to get rid of old way in separate branch and just throw error if core is incompatible

surely drush should align as well

[andypost]

I think the option 3 but with 4.0 release

[andypost]

also depending on version you can use templates vs templates_attributes directory

[weitzman]

Looks like we are cruising along toward Option 4?

[Chi-teck]

Plugin generators will be updated in DCG 4.x. See #156 for details.