Add length validation for tags in NodeForm

We get the following exception when adding a tag that is too long:

Drupal\Core\Entity\EntityStorageException: SQLSTATE[22001]: String data, right truncated: 1406 Data too long for column 'name' at row 1: INSERT INTO {taxonomy_term_field_data} (tid, vid, langcode, name, description__value, description__format, weight, changed, default_langcode) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8); Array ( [:db_insert_placeholder_0] => 8 [:db_insert_placeholder_1] => tags [:db_insert_placeholder_2] => en [:db_insert_placeholder_3] => volutpat tortor. Aenean sit amet risus ante. Etiam sit amet nisi id risus interdum congue. Duis ut erat non orci pulvinar ultricies vitae ut nulla. Nullam vehicula hendrerit pretium. Nullam sit amet sapien et massa gravida venenatis eu sit amet ipsum. Nulla dapibus metus lorem [:db_insert_placeholder_4] => [:db_insert_placeholder_5] => [:db_insert_placeholder_6] => 0 [:db_insert_placeholder_7] => 1442409979 [:db_insert_placeholder_8] => 1 ) in Drupal\Core\Entity\Sql\SqlContentEntityStorage->save() (line 757 of core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php).

We need to add a validation for this.