LibWeb: Move SVGPathElement methods into SVGGeometryElement

From the spec:

> Interface SVGGeometryElement represents SVG elements whose rendering
> is defined by geometry with an equivalent path, and which can be
> filled and stroked. This includes paths and the basic shapes.

- https://svgwg.org/svg2-draft/types.html#InterfaceSVGGeometryElement

Making them all create an SVGPathBox, and return a Path from get_path(),
means we can implement the "basic shapes" using the path system we
already have. :^)

Userland/Libraries/LibWeb/SVG/SVGGeometryElement.h

@@ -10,10 +10,15 @@
 
 namespace Web::SVG {
 
+// https://svgwg.org/svg2-draft/types.html#InterfaceSVGGeometryElement
 class SVGGeometryElement : public SVGGraphicsElement {
 public:
     using WrapperType = Bindings::SVGGeometryElementWrapper;
 
+    virtual RefPtr<Layout::Node> create_layout_node(NonnullRefPtr<CSS::StyleProperties>) override;
+
+    virtual Gfx::Path& get_path() = 0;
+
 protected:
     SVGGeometryElement(DOM::Document& document, QualifiedName qualified_name);
 };