Avoid t() calls, instead use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t()

Problem/Motivation

$ phpcs --standard=DrupalPractice .

FILE: /do_username/src/Plugin/Field/FieldType/DrupalOrgUsernameItem.php
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FOUND 0 ERRORS AND 2 WARNINGS AFFECTING 2 LINES
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 131 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
 134 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
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FILE: /do_username/src/Plugin/Field/FieldWidget/DrupalOrgUsernameWidget.php
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FOUND 0 ERRORS AND 8 WARNINGS AFFECTING 8 LINES
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 41 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
 48 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
 50 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
 54 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
 56 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
 68 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
 70 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
 73 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
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User interface changes

NONE

API changes

NONE

Data model changes

NONE