DataDifferencer::getObjectDisplay should use CMSThumbnail to limit max size of images in diffs

[sabina-talipova]

Description

Investigate the possibility of using the Image::CMSThumbnail method instead of Image::getTag.
"Use CMSThumbnail instead to limit max size, blocked by DataDifferencerTest and GC not playing nice with mocked images".
See

silverstripe-versioned/src/DataDifferencer.php

Lines 184 to 199 in f5cd4ed

	protected function getObjectDisplay($object = null)
	{
	if (!$object || !$object->isInDB()) {
	return '';
	}
	// Use image tag
	// TODO Use CMSThumbnail instead to limit max size, blocked by DataDifferencerTest and GC
	// not playing nice with mocked images
	if ($object instanceof Image) {
	return $object->getTag();
	}
	// Format title
	return $object->obj('Title')->forTemplate();
	}