Unable to order transitions if there are more than 20

Nice catch, bumping the available transition weights from 20 to 200 makes a lot of sense. A couple of things:

• Do you think we should bump the number of allowed states at the same time?
• Do we think we can simply assert the weight select boxes have the correct ranges of numbers in them, or use some weights in the earlier test case between -100 and 100? We want to avoid retesting abstractions we are depending on, in this case '#type' => 'weight'.

Maybe something as simple as:

    $this->assertSession()
      ->selectExists('transitions[create_new_draft][weight]')
      ->selectOption('100');
    $this->assertSession()
      ->selectExists('transitions[create_new_draft][weight]')
      ->selectOption('-100');

Looks great, thanks.

+++ b/core/modules/workflows/src/Form/WorkflowEditForm.php
@@ -193,6 +193,7 @@ public function form(array $form, FormStateInterface $form_state) {
           '#default_value' => $transition->weight(),
           '#attributes' => ['class' => ['transition-weight']],

Why not count the number of transitions and use that? Any limit seems a bit arbitrary.

In blocks we do:

    // Weights range from -delta to +delta, so delta should be at least half
    // of the amount of blocks present. This makes sure all blocks in the same
    // region get an unique weight.
    $weight_delta = round(count($entities) / 2);

Testing.

1. Confirming undesirable behavior by enabling moderation/workflows, adding a bunch of states, getting up to 21 transitions, and attempting to reorder: ...
2. Actually, you need 22 transitions, because there are 21 weightings including 0. Adding another.
3. Successfully reproduced. Ended up in a situation where alphabetical ordering took over for my last 2 items.
4. Applying patch: curl -l https://www.drupal.org/files/issues/2018-04-13/workflow-transition-ordering-2939634-9.patch | git apply -v
5. Applies clean.
6. drush cr
7. Refreshing and resting using my existing states and transitions: success, I am able to reorder my final 2 items, and showing the row weights confirms the new behavior. Providing a screenshot below showing row weights where I moved "Create New Draft" to come before "5 -> 4", even though "5 -> 4" has alphabetical priority. Also providing a screenshot of the "-11" delta that got used in the process.

Moving to RTBC.

Committed and pushed 6a74240ce3 to 8.6.x and ffaf769407 to 8.5.x. Thanks!

Backported to 8.5.x as a bugfix.