LibGfx+LibWeb: Add ImmutableBitmap for images bitmap caching in painter

Before this change, we used Gfx::Bitmap to represent both decoded
images that are not going to be mutated and bitmaps corresponding
to canvases that could be mutated.

This change introduces a wrapper for bitmaps that are not going to be
mutated, so the painter could do caching: texture caching in the case
of GPU painter and potentially scaled bitmap caching in the case of CPU
painter.

Userland/Libraries/LibGfx/ImmutableBitmap.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2023, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Forward.h>
+#include <AK/RefCounted.h>
+#include <LibGfx/Bitmap.h>
+#include <LibGfx/Forward.h>
+#include <LibGfx/Rect.h>
+
+namespace Gfx {
+
+class ImmutableBitmap final : public RefCounted<ImmutableBitmap> {
+public:
+    static NonnullRefPtr<ImmutableBitmap> create(NonnullRefPtr<Bitmap> bitmap);
+
+    ~ImmutableBitmap() = default;
+
+    Bitmap const& bitmap() const { return *m_bitmap; }
+
+    size_t width() const { return m_bitmap->width(); }
+    size_t height() const { return m_bitmap->height(); }
+
+    IntRect rect() const { return m_bitmap->rect(); }
+    IntSize size() const { return m_bitmap->size(); }
+
+    size_t id() const { return m_id; }
+
+private:
+    NonnullRefPtr<Bitmap> m_bitmap;
+    size_t m_id;
+
+    explicit ImmutableBitmap(NonnullRefPtr<Bitmap> bitmap);
+};
+
+}