Bug 1700640 - Map width and height to aspect-ratio in <canvas>, <input type=image>, and <video>. r=boris

As per https://html.spec.whatwg.org/#attributes-for-embedded-content-and-images:

> The width and height attributes map to the aspect-ratio property on
> img, canvas, and video elements, and input elements with a type
> attribute in the Image Button state.

See https://github.com/whatwg/html/issues/6527 for the parsing issue
with canvas and zero. For now allow both behaviors in the tests.

We also remove the width-and-height-map-to-aspect-ratio pref, as it is
true everywhere and has been for a while.

Differential Revision: https://phabricator.services.mozilla.com/D109618

dom/html/HTMLInputElement.cpp

@@ -5133,8 +5133,8 @@ void HTMLInputElement::ImageInputMapAttributesIntoRule(
                                                                  aDecls);
   nsGenericHTMLFormElementWithState::MapImageMarginAttributeInto(aAttributes,
                                                                  aDecls);
-  nsGenericHTMLFormElementWithState::MapImageSizeAttributesInto(aAttributes,
-                                                                aDecls);
+  nsGenericHTMLFormElementWithState::MapImageSizeAttributesInto(
+      aAttributes, aDecls, MapAspectRatio::Yes);
   // Images treat align as "float"
   nsGenericHTMLFormElementWithState::MapImageAlignAttributeInto(aAttributes,
                                                                 aDecls);