MDL-75692 core_h5p: Debounce resize events

* Make sure that we don't call the resize event too often to
avoid infinite loop when content is auto resizing (fonts for example)

h5p/js/embed.js

@@ -231,7 +231,7 @@ document.onreadystatechange = async() => {
             } else {
                 H5PEmbedCommunicator.send('hello');
             }
-        }, 0);
+        }, 250);
     });
 
     // Get emitted xAPI data.