Make category translatable

Problem/Motivation

In all Tamper plugins the category is currently defined as a plain string. But according to the annotation, it should be a translatable string:

/**
 * The category under which the tamper plugin should be listed in the UI.
 *
 * @var \Drupal\Core\Annotation\Translation
 *
 * @ingroup plugin_translatable
 */
public $category = '';

Proposed resolution

Go through all Tamper plugins and add @Translation() to the category property.

Remaining tasks

• Implement solution
• Check in the UI if category's get translated.
• Commit.

User interface changes

Category's get translated in the UI. In some languages, some plugins may be displayed higher or lower on the list.

API changes

Technically not an API change, but category should now always be translatable.

Data model changes

None.