LibWeb: Sketch out a very basic SVG <clipPath> element

This element doesn't actually support anything at the moment, but it
still massively speeds up painting performance on Wikipedia! :^)

How? Because we no longer paint SVG <path> elements found inside
<clipPath> elements. SVGClipPathElement::create_layout_node() returns
nullptr which stops the layout tree builder from recursing further into
the subtree, and so the <path> element never gets a layout or paint box.

Mousing over Wikipedia now barely break 50% CPU usage on my machine :^)

Userland/Libraries/LibWeb/SVG/SVGClipPathElement.cpp

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/SVG/SVGClipPathElement.h>
+
+namespace Web::SVG {
+
+SVGClipPathElement::SVGClipPathElement(DOM::Document& document, DOM::QualifiedName qualified_name)
+    : SVGElement(document, move(qualified_name))
+{
+}
+
+SVGClipPathElement::~SVGClipPathElement()
+{
+}
+
+RefPtr<Layout::Node> SVGClipPathElement::create_layout_node(NonnullRefPtr<CSS::StyleProperties>)
+{
+    return nullptr;
+}
+
+}

Userland/Libraries/LibWeb/SVG/SVGClipPathElement.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/SVG/SVGElement.h>
+
+namespace Web::SVG {
+
+class SVGClipPathElement final : public SVGElement {
+public:
+    using WrapperType = Bindings::SVGClipPathElementWrapper;
+
+    SVGClipPathElement(DOM::Document&, DOM::QualifiedName);
+    virtual ~SVGClipPathElement();
+
+    virtual RefPtr<Layout::Node> create_layout_node(NonnullRefPtr<CSS::StyleProperties>) override;
+};
+
+}

Userland/Libraries/LibWeb/SVG/SVGClipPathElement.idl

@@ -0,0 +1,7 @@
+[Exposed=Window]
+interface SVGClipPathElement : SVGElement {
+
+    // FIXME: readonly attribute SVGAnimatedEnumeration clipPathUnits;
+    // FIXME: readonly attribute SVGAnimatedTransformList transform;
+
+};

Userland/Libraries/LibWeb/SVG/TagNames.h

@@ -24,6 +24,7 @@ namespace Web::SVG::TagNames {
 
 #define ENUMERATE_SVG_TAGS             \
     ENUMERATE_SVG_GRAPHICS_TAGS        \
+    __ENUMERATE_SVG_TAG(clipPath)      \
     __ENUMERATE_SVG_TAG(desc)          \
     __ENUMERATE_SVG_TAG(foreignObject) \
     __ENUMERATE_SVG_TAG(script)        \