LibWeb: Factor out HTMLOrSVGElement

This is a mixin in the IDL, so let's treat it as a mixin in our code and
let both SVGElement and MathMLElement reuse the implementations that we
wrote for HTMLElement.

Userland/Libraries/LibWeb/HTML/HTMLOrSVGElement.cpp

@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2024, Jelle Raaijmakers <jelle@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/HTML/Focus.h>
+#include <LibWeb/HTML/HTMLElement.h>
+#include <LibWeb/HTML/HTMLOrSVGElement.h>
+#include <LibWeb/MathML/MathMLElement.h>
+#include <LibWeb/SVG/SVGElement.h>
+
+namespace Web::HTML {
+
+// https://html.spec.whatwg.org/multipage/dom.html#dom-dataset-dev
+template<typename ElementBase>
+JS::NonnullGCPtr<DOMStringMap> HTMLOrSVGElement<ElementBase>::dataset()
+{
+    if (!m_dataset)
+        m_dataset = DOMStringMap::create(*static_cast<ElementBase*>(this));
+    return *m_dataset;
+}
+
+// https://html.spec.whatwg.org/multipage/interaction.html#dom-focus
+template<typename ElementBase>
+void HTMLOrSVGElement<ElementBase>::focus()
+{
+    // FIXME: below are the focus(options) steps, also implement focus()
+
+    // 1. If the element is marked as locked for focus, then return.
+    if (m_locked_for_focus)
+        return;
+
+    // 2. Mark the element as locked for focus.
+    m_locked_for_focus = true;
+
+    // 3. Run the focusing steps for the element.
+    run_focusing_steps(static_cast<ElementBase*>(this));
+
+    // FIXME: 4. If the value of the preventScroll dictionary member of options is false,
+    //           then scroll the element into view with scroll behavior "auto",
+    //           block flow direction position set to an implementation-defined value,
+    //           and inline base direction position set to an implementation-defined value.
+
+    // 5. Unmark the element as locked for focus.
+    m_locked_for_focus = false;
+}
+
+// https://html.spec.whatwg.org/multipage/interaction.html#dom-blur
+template<typename ElementBase>
+void HTMLOrSVGElement<ElementBase>::blur()
+{
+    // The blur() method, when invoked, should run the unfocusing steps for the element on which the method was called.
+    run_unfocusing_steps(static_cast<ElementBase*>(this));
+
+    // User agents may selectively or uniformly ignore calls to this method for usability reasons.
+}
+
+template<typename ElementBase>
+void HTMLOrSVGElement<ElementBase>::visit_edges(JS::Cell::Visitor& visitor)
+{
+    visitor.visit(m_dataset);
+}
+
+template class HTMLOrSVGElement<HTMLElement>;
+template class HTMLOrSVGElement<MathML::MathMLElement>;
+template class HTMLOrSVGElement<SVG::SVGElement>;
+
+}