ACP2E-2266: set itemprop for main product image with or w/o fotorama loading

Author: alzota

app/code/Magento/Catalog/view/frontend/templates/product/view/gallery.phtml

@@ -32,6 +32,7 @@ $mainImageData = $mainImage ?
     <img
         alt="main product photo"
         class="gallery-placeholder__image"
+        itemprop="image"
         src="<?= /* @noEscape */ $mainImageData ?>"
     />
 </div>

lib/web/mage/gallery/gallery.js

@@ -314,6 +314,10 @@ define([
             $fotoramaElement.fotorama(config);
             $fotoramaElement.find('.fotorama__stage__frame.fotorama__active')
                     .one('f:load', function () {
+                        // Mark itemprop on main image
+                        $fotoramaElement
+                            .find('.fotorama__stage__frame.fotorama__active img')
+                            .attr('itemprop', 'image');
                         // Remove placeholder when main gallery image loads.
                         $element.find('.gallery-placeholder__image').remove();
                         $element