Optimization for media.filter.preview

As pointed out by @Berdir over at #3202501-29: webp support for drimage →

Currently it is unclear what the issue is and what the solution does.
We need more info from the creator of the patch in the original issue.

+++ b/src/Plugin/Field/FieldFormatter/DrImageFormatter.php
@@ -301,6 +304,11 @@ class DrImageFormatter extends ImageFormatter {
 
+      // Media embed preview workaround
+      if (\Drupal::routeMatch()->getRouteName() === 'media.filter.preview') {
+        $elements[$delta]['#data']['media_preview'] = TRUE;
+      }