Ensure that the lazy loading attribute is ignored on script-disabled documents

From #33534 (closed): Firefox 75 added support for the loading attribute of HTML <img> elements. This string value can be used to specify that the image should be lazily loaded, by setting its value to lazy. This could allow sites to track a user's scrolling behavior and use it for fingerprinting. Maybe that is OK since:

1. Similar tracking is already possible via other mechanisms when JavaScript is enabled.
2. The lazy loading feature is supposedly disabled when JavaScript is disabled.

We should confirm.

https://bugzilla.mozilla.org/show_bug.cgi?id=1542784
"Support <img loading="lazy"> lazy-loading"