Load a plugin definition? I want to load a plugin definition by its string id within a controller extending ControllerBase. What is the relevant service or class I am looking for?
You can use the plugin manager to fetch a plugin. You only need to find the correct plugin manager service:

$type = \Drupal::service('plugin.manager.service'); // Fill your own plugin manager service.
$plugin_definition = $type-&gt;getDefinition('plugin_id'); // Fill needed plugin id.