Method getPluginResponse should be in AiContentSuggestionsPluginBase class and not in external service
<!-- Please search existing work items before filing to avoid duplicates. -->
<!-- Also check open feature request work items to avoid duplicating existing proposals. -->
## Summary
To make the code more readable and to have all relevant functionality of the plugins inside plugin classes, there is a suggestion to refactor the plugins inside ai_content_suggestion module.
## Problem
At the moment `getPluginResponse` method that is used in the ajax callback inside AI Content Suggestion plugins is placed in the external service. This causes unnecessary static calls of the plugin manager service.
## Proposed solution *(optional)*
Instead it should be inside the base class. This will also allow to not have this method as static and use dependency injection.
Also the code that is related to the plugin will be in one class.
## Workaround *(optional)*
<!-- Describe any workaround you are currently using, or state that none exists. This helps maintainers assess priority. -->
## Affected modules / components *(optional)*
<!--
List the sub-modules or areas of the AI module this request relates to.
Examples: ai_api_explorer, ai_agent, providers/ai_provider_openai, AI Dashboard UI
-->
<!-- If this issue description was significantly AI-generated (entire sections, not autocomplete), please note it in a comment below. See https://www.drupal.org/docs/develop/issues/issue-procedures-and-etiquette/policy-on-the-use-of-ai-when-contributing-to-drupal -->
issue