LibWeb: Generalize support for dimension attributes

Rather than each element which supports dimension attributes needing to
implement parsing the attributes and setting the appropriate style, we
can generalize this functionality. This will also make each element more
closely resemble the spec text, as we will be effectively declaring, for
example, "The img element supports dimension attributes" in code.

Userland/Libraries/LibWeb/HTML/HTMLImageElement.h

@@ -107,6 +107,9 @@ private:
 
     virtual void apply_presentational_hints(CSS::StyleProperties&) const override;
 
+    // https://html.spec.whatwg.org/multipage/embedded-content.html#the-img-element:dimension-attributes
+    virtual bool supports_dimension_attributes() const override { return true; }
+
     virtual JS::GCPtr<Layout::Node> create_layout_node(NonnullRefPtr<CSS::StyleProperties>) override;
 
     virtual void did_set_viewport_rect(CSSPixelRect const&) override;