public OverviewTerms::submitForm(array &$form, FormStateInterface $form_state)
Form submission handler.
Rather than using a textfield or weight field, this form depends entirely upon the order of form elements on the page to determine new weights.
Because there might be hundreds or thousands of taxonomy terms that need to be ordered, terms are weighted from 0 to the number of terms in the vocabulary, rather than the standard -10 to 10 scale. Numbers are sorted lowest to highest, but are not