Style selection always visible

The only reason we stopped just using $form is to fix some problems, lets check this with @mbo next week.

#3: Yes, we didn't want to produce any additional markup if there are no styles to select. That was the reason to switch away from $form and use $build.

+++ b/src/Plugin/paragraphs/Behavior/ParagraphsStylePlugin.php
@@ -70,6 +70,9 @@ class ParagraphsStylePlugin extends ParagraphsBehaviorBase implements ContainerF
+    // The form array only contains the group information that is needed for
+    // the behaviors tab to work properly.
+    $build = $form;

Either we do this here for the style plugin only, or we append the plugin behavior form array in Drupal\paragraphs\Plugin\Field\FieldWidget\ParagraphsWidget::formElement() as $element['behavior_plugins'][$plugin_id] += $plugin_form;?

Related issues: #2971115: Do not print behavior form if there is nothing a plugin can do, #3002419: Base buildBehaviorForm should not add markup for plugins with no behavior form

Working on tests for this. :)

I was checking the code of other plugins and it seems we always used the form variable to add all the plugin elements. I think is better to make them all equal to making it easier to change later. (e.g. not adding any markup at all if there are no plugins).

My bad. :(

Yes, lets revert that change for now, we do have test coverage now in case we decide to improve that later, then we could also add test coverage for the specific problem that solves in regards to the markup...