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.cpp

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2023, Gregory Bertilson <Zaggy1024@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "Reader.h"
+
+namespace Gfx::ISOBMFF {
+
+ErrorOr<Reader> Reader::create(MaybeOwned<SeekableStream> stream)
+{
+    return Reader(move(stream));
+}
+
+ErrorOr<BoxList> Reader::read_entire_file()
+{
+    BoxList top_level_boxes;
+
+    while (!m_stream->is_eof()) {
+        auto box_header = TRY(read_box_header(*m_stream));
+        BoxStream box_stream { *m_stream, box_header.contents_size };
+
+        switch (box_header.type) {
+        case BoxType::FileTypeBox:
+            TRY(top_level_boxes.try_append(TRY(FileTypeBox::create_from_stream(box_stream))));
+            break;
+        default:
+            TRY(top_level_boxes.try_append(TRY(UnknownBox::create_from_stream(box_header.type, box_stream))));
+            break;
+        }
+
+        if (!box_stream.is_eof())
+            return Error::from_string_literal("Reader did not consume all data");
+    }
+    return top_level_boxes;
+}
+
+}