Convert the procedural hooks to OOP hook classes in the Varbase Content Planner module

Problem/Motivation

The Varbase Content Planner submodule (part of the Varbase Workflow project) currently implements its hooks as procedural functions in varbase_content_planner.module. Drupal 11 provides object-oriented hooks via the #[Hook] attribute (see the OOP hooks change record), which are autoloaded, easier to test, and support dependency injection.

Steps to reproduce

N/A — this is a code-quality refactoring task, not a defect. To see the current state:

1. Open varbase_content_planner.module in the varbase_content_planner submodule.
2. Note that hook_theme(), hook_theme_suggestions_HOOK_alter() (for item_list) and hook_toolbar_alter() are implemented procedurally rather than as OOP #[Hook] methods.

Proposed resolution

Move the procedural hook implementations (hook_theme, hook_theme_suggestions_HOOK_alter for item_list, and hook_toolbar_alter) into a new object-oriented hook class \Drupal\varbase_content_planner\Hook\VarbaseContentPlannerHooks, using the #[Hook] attribute. hook_preprocess_varbase_item_list() is kept procedural in the .module file.

Remaining tasks

• ✅ File an issue about this project
• ✅ Addition/Change/Update/Fix to this project
• ✅ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ➖ Developer Documentation support on feature change/addition
• ➖ User Guide Documentation support on feature change/addition
• ➖ UX/UI designer responsibilities
• ➖ Accessibility and Readability
• ✅ Reviewed by a human
• ✅ Code review by maintainers
• ✅ Full testing and approval
• ✅ Credit contributors
• ✅ Review with the product owner
• ✅ Update Release Notes
• ✅ Release varbase-9.2.0, varbase_workflow-2.2.0

User interface changes

• N/A — internal refactor only, no user-facing UI change.

API changes

• None. These are standard hooks invoked by Drupal core only; converting them to the OOP #[Hook] pattern (https://www.drupal.org/node/3442349) does not change any public API or hook contract.

Data model changes

• N/A

Release notes snippet

• task: #3608325 Convert the procedural hooks to OOP hook classes in the Varbase Workflow module