How to translate text in annotations in Drupal 8

Classes with annotations serve to define entity types, plugins and so on. Annotations are not executable code as-is, so we need a specific syntax to mark strings to be translated. The @Translation() wrapper serves this purpose. It will run the text through t() when the annotation is evaluated.

Example:

/**
 * Defines the file entity class.
 *
 * @EntityType(
 *   id = "file",
 *   label = @Translation("File"),
 *   ....
 */
class File {
 }

Example with context:

/**
 * Defines the file entity class.
 *
 * @EntityType(
 *   id = "file",
 *   label = @Translation("Text in context", context="Name of context"),
 *   ....
 */
class File {
 }