LibWeb: Make DecodedImageData an abstract class

The existing implementation moves down into a new subclass called
AnimatedBitmapDecodedImageData.

The purpose of this change is to create an extension point where we can
plug in an SVG renderer. :^)

Userland/Libraries/LibWeb/HTML/AnimatedBitmapDecodedImageData.cpp

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2023, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibGfx/Bitmap.h>
+#include <LibWeb/HTML/AnimatedBitmapDecodedImageData.h>
+
+namespace Web::HTML {
+
+ErrorOr<NonnullRefPtr<AnimatedBitmapDecodedImageData>> AnimatedBitmapDecodedImageData::create(Vector<Frame>&& frames, size_t loop_count, bool animated)
+{
+    return adopt_nonnull_ref_or_enomem(new (nothrow) AnimatedBitmapDecodedImageData(move(frames), loop_count, animated));
+}
+
+AnimatedBitmapDecodedImageData::AnimatedBitmapDecodedImageData(Vector<Frame>&& frames, size_t loop_count, bool animated)
+    : m_frames(move(frames))
+    , m_loop_count(loop_count)
+    , m_animated(animated)
+{
+}
+
+AnimatedBitmapDecodedImageData::~AnimatedBitmapDecodedImageData() = default;
+
+RefPtr<Gfx::Bitmap const> AnimatedBitmapDecodedImageData::bitmap(size_t frame_index) const
+{
+    if (frame_index >= m_frames.size())
+        return nullptr;
+    return m_frames[frame_index].bitmap;
+}
+
+int AnimatedBitmapDecodedImageData::frame_duration(size_t frame_index) const
+{
+    if (frame_index >= m_frames.size())
+        return 0;
+    return m_frames[frame_index].duration;
+}
+
+Optional<int> AnimatedBitmapDecodedImageData::natural_width() const
+{
+    return m_frames.first().bitmap->width();
+}
+
+Optional<int> AnimatedBitmapDecodedImageData::natural_height() const
+{
+    return m_frames.first().bitmap->height();
+}
+
+}