Show image thumbnail for image plugin

We should also create a separate issue about exif data export diff visualisation (on exiftool, if present) and connect the issues.

+++ b/src/Plugin/diff/Field/ImageFieldBuilder.php
@@ -57,6 +57,19 @@ class ImageFieldBuilder extends FieldDiffBuilderBase {
+            '#style_name' => 'thumbnail',

Is thumbnail guaranteed to exist? I doubt.

We need to decide if we are using some style that is configured or if we need to have this configurable such as with the diff plugin setting. But i would try to avoid that.

So checked, yeah the thumbnail image style can be deleted.

But the form display has the preview image style configured. We should simply use that one.

I guess, we should offer a new setting to display the image (default on), right?

About the check for 'thumbnail' -- shouldn't it be '#thumbnail'?

This is pretty invasive for DiffEntityComparision. I wonder how to deal with other advanced elements in diff.

+++ b/src/Plugin/diff/Field/ImageFieldBuilder.php
@@ -57,6 +57,21 @@ class ImageFieldBuilder extends FieldDiffBuilderBase {
+              '#style_name' => 'thumbnail',

Let's first focus on picking the right image style. As stated, the preview style is configured in manage form display.

Then we can discuss about how much alteration makes sense and is acceptable in the current lifecycle.

1. +++ b/src/Plugin/diff/Field/ImageFieldBuilder.php
   @@ -57,6 +57,22 @@ class ImageFieldBuilder extends FieldDiffBuilderBase {
   +        if ($this->configuration['compare_alt_field']) {
   

   compare_alt_field => show_thumbnail
   And this shows why we need test coverage... ;-)

2. +++ b/src/Plugin/diff/Field/ImageFieldBuilder.php
   @@ -57,6 +57,22 @@ class ImageFieldBuilder extends FieldDiffBuilderBase {
   +              $image_style[$field_key]['#thumbnail'] = array(
   ...
   +              $result = array_merge($result, $image_style);
   

   Why not just $result[$field_key]['#thumbnail']

And then we need to discuss the APIs and how we make this clean for other advanced cases.

I'm kinda missing the image in the Unified fields layout.
Added some comments and committed!