LibWeb/CSS: Implement CSSTransformComponent

This is a base type for the various transform functions.

CSSMatrixComponent's to_string() can throw exceptions, so to_string() is
implemented that way. https://github.com/w3c/fxtf-drafts/issues/611

+9 WPT subtests.

Libraries/LibWeb/CSS/CSSTransformComponent.h

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2025, Sam Atkins <sam@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/Bindings/PlatformObject.h>
+
+namespace Web::CSS {
+
+// https://drafts.css-houdini.org/css-typed-om-1/#csstransformcomponent
+class CSSTransformComponent : public Bindings::PlatformObject {
+    WEB_PLATFORM_OBJECT(CSSTransformComponent, Bindings::PlatformObject);
+    GC_DECLARE_ALLOCATOR(CSSTransformComponent);
+
+public:
+    enum class Is2D : u8 {
+        No,
+        Yes,
+    };
+
+    virtual void initialize(JS::Realm&) override;
+    virtual ~CSSTransformComponent() override;
+
+    virtual WebIDL::ExceptionOr<Utf16String> to_string() const = 0;
+
+    bool is_2d() const { return m_is_2d; }
+    virtual void set_is_2d(bool value) { m_is_2d = value; }
+
+    virtual WebIDL::ExceptionOr<GC::Ref<Geometry::DOMMatrix>> to_matrix() const = 0;
+
+protected:
+    explicit CSSTransformComponent(JS::Realm&, Is2D is_2d);
+
+private:
+    bool m_is_2d;
+};
+
+}