LibWeb: Add initial support for SVG <textPath>

This patch adds basic support for the SVG `<textPath>`, so it supports
placing text along a path, but none of the extra attributes for
controlling the layout of the text. This is enough to correctly display
the MDN example.

Userland/Libraries/LibWeb/SVG/SVGTextPathElement.cpp

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2023, MacDue <macdue@dueutil.tech>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/URL.h>
+#include <LibWeb/Layout/SVGTextPathBox.h>
+#include <LibWeb/SVG/AttributeNames.h>
+#include <LibWeb/SVG/SVGTextPathElement.h>
+
+namespace Web::SVG {
+
+JS_DEFINE_ALLOCATOR(SVGTextPathElement);
+
+SVGTextPathElement::SVGTextPathElement(DOM::Document& document, DOM::QualifiedName qualified_name)
+    : SVGTextContentElement(document, move(qualified_name))
+{
+}
+
+JS::GCPtr<SVGGeometryElement const> SVGTextPathElement::path_or_shape() const
+{
+    auto href = get_attribute(AttributeNames::href);
+    if (!href.has_value())
+        return {};
+    auto url = document().url().complete_url(*href);
+    return try_resolve_url_to<SVGGeometryElement const>(url);
+}
+
+void SVGTextPathElement::initialize(JS::Realm& realm)
+{
+    Base::initialize(realm);
+    set_prototype(&Bindings::ensure_web_prototype<Bindings::SVGTextPathElementPrototype>(realm, "SVGTextPathElement"_fly_string));
+}
+
+JS::GCPtr<Layout::Node> SVGTextPathElement::create_layout_node(NonnullRefPtr<CSS::StyleProperties> style)
+{
+    return heap().allocate_without_realm<Layout::SVGTextPathBox>(document(), *this, move(style));
+}
+
+};

Userland/Libraries/LibWeb/SVG/SVGTextPathElement.h

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2023, MacDue <macdue@dueutil.tech>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/SVG/SVGGeometryElement.h>
+#include <LibWeb/SVG/SVGTextContentElement.h>
+
+namespace Web::SVG {
+
+// https://svgwg.org/svg2-draft/text.html#TextPathElement
+class SVGTextPathElement : public SVGTextContentElement {
+    WEB_PLATFORM_OBJECT(SVGTextPathElement, SVGTextContentElement);
+    JS_DECLARE_ALLOCATOR(SVGTextPathElement);
+
+public:
+    virtual JS::GCPtr<Layout::Node> create_layout_node(NonnullRefPtr<CSS::StyleProperties>) override;
+
+    JS::GCPtr<SVGGeometryElement const> path_or_shape() const;
+
+protected:
+    SVGTextPathElement(DOM::Document&, DOM::QualifiedName);
+
+    virtual void initialize(JS::Realm&) override;
+};
+
+}

Userland/Libraries/LibWeb/SVG/SVGTextPathElement.idl

@@ -0,0 +1,23 @@
+#import <SVG/SVGTextContentElement.idl>
+#import <SVG/SVGURIReference.idl>
+
+// https://svgwg.org/svg2-draft/text.html#InterfaceSVGTextPathElement
+[Exposed=Window]
+interface SVGTextPathElement : SVGTextContentElement {
+
+  // textPath Method Types
+  const unsigned short TEXTPATH_METHODTYPE_UNKNOWN = 0;
+  const unsigned short TEXTPATH_METHODTYPE_ALIGN = 1;
+  const unsigned short TEXTPATH_METHODTYPE_STRETCH = 2;
+
+  // textPath Spacing Types
+  const unsigned short TEXTPATH_SPACINGTYPE_UNKNOWN = 0;
+  const unsigned short TEXTPATH_SPACINGTYPE_AUTO = 1;
+  const unsigned short TEXTPATH_SPACINGTYPE_EXACT = 2;
+
+  // FIXME: [SameObject] readonly attribute SVGAnimatedLength startOffset;
+  // FIXME: [SameObject] readonly attribute SVGAnimatedEnumeration method;
+  // FIXME: [SameObject] readonly attribute SVGAnimatedEnumeration spacing;
+};
+
+SVGTextPathElement includes SVGURIReference;

Userland/Libraries/LibWeb/SVG/SVGURIReference.idl

@@ -0,0 +1,3 @@
+interface mixin SVGURIReference {
+  // FIXME: [SameObject] readonly attribute SVGAnimatedString href;
+};

Userland/Libraries/LibWeb/SVG/TagNames.h

@@ -22,6 +22,7 @@ namespace Web::SVG::TagNames {
     __ENUMERATE_SVG_TAG(rect)       \
     __ENUMERATE_SVG_TAG(svg)        \
     __ENUMERATE_SVG_TAG(text)       \
+    __ENUMERATE_SVG_TAG(textPath)   \
     __ENUMERATE_SVG_TAG(tspan)
 
 #define ENUMERATE_SVG_TAGS              \