Manually add loading=lazy in certain image tags loaded by WordPress

[superpoincare]

in #44427, the feature to lazy load images by default was added.

However it doesn't work on all images, only ones filterable with certain filters.

One such example is the image /wp-includes/images/rss.png loaded by the RSS widget.

Such images need a loading=lazy attribute added manually.

[sabernhardt]

For the RSS widget icon, the lazy-loading attribute is included in my patch on #52224.

These two functions also create markup for images in the wp-includes directory:

• the_embed_site_title
• translate_smiley

[Mista-Flo]

That was fixed in this ticket: #52224