LibGfx: Add initial ISO BMFF parsing and a utility to print file info

Currently, the `isobmff` utility will only print the media file type
info from the FileTypeBox (major brand and compatible brands), as well
as the names and sizes of top-level boxes.

Userland/Libraries/LibGfx/ImageFormats/ISOBMFF/Reader.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2023, Gregory Bertilson <Zaggy1024@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/MaybeOwned.h>
+#include <AK/Stream.h>
+
+#include "Boxes.h"
+
+namespace Gfx::ISOBMFF {
+
+class Reader {
+public:
+    static ErrorOr<Reader> create(MaybeOwned<SeekableStream> stream);
+
+    ErrorOr<BoxList> read_entire_file();
+
+    ErrorOr<BrandIdentifier> get_major_brand();
+    ErrorOr<Vector<BrandIdentifier>> get_minor_brands();
+
+private:
+    Reader(MaybeOwned<SeekableStream> stream)
+        : m_stream(move(stream))
+    {
+    }
+
+    ErrorOr<void> parse_initial_data();
+
+    MaybeOwned<SeekableStream> m_stream;
+};
+
+}