LibGfx: Add start of an ICC profile writer

For now, this can write the profile header.

`icc` refuses to dump its contents since the required copyrightTag,
profileDescriptionTag, and required per-device-class tags are missing,
but it looks ok in a hex editor.

Userland/Libraries/LibGfx/ICC/BinaryWriter.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2023, Nico Weber <thakis@chromium.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/ByteBuffer.h>
+
+namespace Gfx::ICC {
+
+class Profile;
+
+// Serializes a Profile object.
+// Ignores the Profile's on_disk_size() and id() and recomputes them instead.
+// Also ignores and the offsets and sizes in tag data.
+// But if the profile has its tag data in tag order and has a computed id,
+// it's a goal that  encode(Profile::try_load_from_externally_owned_memory(bytes) returns `bytes`.
+// Unconditionally computes a Profile ID (which is an MD5 hash of most of the contents, see Profile::compute_id()) and writes it to the output.
+ErrorOr<ByteBuffer> encode(Profile const&);
+
+}