Fix all viewElements() compatibility with FormatterInterface::viewElements

[otarza]

After adding addthis field to a content type and try to visit form display I get following error:

PHP Fatal error: Declaration of Drupal\\addthis\\Plugin\\Field\\FieldFormatter\\AddThisBasicButtonFormatter::viewElements() must be compatible with Drupal\\Core\\Field\\FormatterInterface::viewElements(Drupal\\Core\\Field\\FieldItemListInterface $items, $langcode) in /modules/contrib/addthis/src/Plugin/Field/FieldFormatter/AddThisBasicButtonFormatter.php on line 26

Fix:

• Add $langcode parameter to viewElements() method of 3 FieldFormatters that are implemented in this module.