LibWeb: Avoid many style invalidations on DOM attribute mutation

Many times, attribute mutation doesn't necessitate a full style
invalidation on the element. However, the conditions are pretty
elaborate, so this first version has a lot of false positives.

We only need to invalidate style when any of these things apply:

1. The change may affect the match state of a selector somewhere.
2. The change may affect presentational hints applied to the element.

For (1) in this first version, we have a fixed list of attribute names
that may affect selectors. We also collect all names referenced by
attribute selectors anywhere in the document.

For (2), we add a new Element::is_presentational_hint() virtual that
tells us whether a given attribute name is a presentational hint.

This drastically reduces style work on many websites. As an example,
https://cnn.com/ is once again browseable.

Libraries/LibWeb/HTML/HTMLIFrameElement.cpp

@@ -60,6 +60,11 @@ void HTMLIFrameElement::attribute_changed(FlyString const& name, Optional<String
         if (name == AttributeNames::srcdoc || (name == AttributeNames::src && !has_attribute(AttributeNames::srcdoc)))
             process_the_iframe_attributes();
     }
+
+    if (name == HTML::AttributeNames::width || name == HTML::AttributeNames::height) {
+        // FIXME: This should only invalidate the layout, not the style.
+        invalidate_style(DOM::StyleInvalidationReason::ElementAttributeChange);
+    }
 }
 
 // https://html.spec.whatwg.org/multipage/iframe-embed-object.html#the-iframe-element:html-element-post-connection-steps