LibWeb: Generalize ImageBox and ImagePaintable for any ImageProvider

They currently assume the DOM node is an HTMLImageElement with respect
to handling the alt attribute. The HTMLInputElement will require the
same behavior.

Userland/Libraries/LibWeb/Layout/ImageProvider.cpp

@@ -0,0 +1,17 @@
+/*
+ * Copyright (c) 2024, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/Layout/ImageBox.h>
+#include <LibWeb/Layout/ImageProvider.h>
+
+namespace Web::Layout {
+
+void ImageProvider::did_update_alt_text(ImageBox& layout_node)
+{
+    layout_node.dom_node_did_update_alt_text({});
+}
+
+}