FileMatcher checks image information if not needed and for non-image files

Problem/Motivation

The matcher has options to display image size and a thumbnail, there are two problems with that. It calls isValid() on every file, even if those options are not enabled and even if they are not images.

For example, that might result in calling isValid() on videos stored on S3, or PDF's or so, resulting in errors/warnings and slow responses.

Proposed resolution

Make two changes:

a) Only call isValid() and do the image factory thing if either of the two options is really enabled.

b) And also only call it if the file extension is supported by the configured toolkit (\Drupal\Core\ImageToolkit\ImageToolkitInterface::getSupportedExtensions(), check how \Drupal\image\Plugin\Field\FieldWidget\ImageWidget::formElement() does that.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet