Replace t() with $this->t() in all plugins for order module.

Problem/Motivation

When attempting to unit test a widget which extends the StringTextfieldWidget the traditional method of mocking the string translation service fails and an error is produced Call to undefined function Drupal\Core\Field\Plugin\Field\FieldWidget\t().

On further inspection many of the plugins extending PluginBase do not utilize $this when calling t().

Proposed resolution

PluginBase is using StringTranslationTrait but many of the child plugins are not utilizing it properly. Use $this->t() instead of t() for string translation calls for all classes extending PluginBase.