Implement abortTranslation

This applies both to aboring on Drupal side and aborting on gengo side.
Either an immediate update should happen, or the state should be pulled on button press.
Both abort states should be in sync to avoid malfunction.

A quick review. No reason to double check. APIs do what they describe and you get a success/error message.

1. +++ b/tmgmt_mygengo.module
   @@ -218,3 +218,48 @@ function tmgmt_mygengo_access_check() {
   +function tmgmt_mygengo_form_tmgmt_job_abort_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
   ...
   +  $form['actions']['submit']['#submit'][] = '_tmgmt_mygengo_abort_form_submit';
   

   This is wrong. It's added to every abort form and also applies if it's not a Gengo provider.
   There is the JobInterface::abortTranslation() and you don't need to attach through a form at all.
   For an example see: tmgmt_oht/src/Plugin/tmgmt/Translator/OhtTranslator.php

2. +++ b/tmgmt_mygengo.module
   @@ -218,3 +218,48 @@ function tmgmt_mygengo_access_check() {
   +          drupal_set_message(t('Unable to abort job @gengo_job_id. It has already been translated or is in progress.', ['@gengo_job_id' => $gengo_job_id]), 'error');
   ...
   +        drupal_set_message(t('Unable to abort job @gengo_job_id. Error: @error', ['@gengo_job_id' => $gengo_job_id, '@error' => $e->getMessage()]), 'error');
   

   That's not really an error. Also we don't use drupal_set_message() in tmgmt. We attach messages to the job.
   The user can abort a job always. But we can not tell the user if it leads to a cancellation at the provider. Also many providers will not refund at all if you cancel.
   Thus, we simply try to cancel the jobs and create a SINGLE message on the job like X of Y messages have been aborted at Gengo.

Yeah looks good now. And yeah, if not all can be stopped, warning would be the best level.
I think you should add to the warning "Gengo does not allow aborting jobs that are already in translation."

I like the presentation almost wanted to commit.

+++ b/src/Plugin/tmgmt/Translator/MyGengoTranslator.php
@@ -558,4 +561,59 @@ class MyGengoTranslator extends TranslatorPluginBase implements ContainerFactory
+          $job_item->addMessage('@count_aborted jobs out of @count_total have been aborted at Gengo. Gengo does not allow aborting jobs that are already in translation.', ['@count_aborted' => $count_aborted, '@count_total' => count($remotes)], 'warning');
...
+          $job_item->addMessage('@count_aborted jobs out of @count_total have been aborted at Gengo.', ['@count_aborted' => $count_aborted, '@count_total' => count($remotes)]);
...
+          $job_item->addMessage('@count_aborted job out of @count_total has been aborted at Gengo. Gengo does not allow aborting jobs that are already in translation.', ['@count_aborted' => $count_aborted, '@count_total' => count($remotes)], 'warning');
...
+          $job_item->addMessage('@count_aborted job out of @count_total has been aborted at Gengo.', ['@count_aborted' => $count_aborted, '@count_total' => count($remotes)]);

I feel blind.
I see only 2 real cases. Why 4?

Works for me now. :-)