LibAudio: Detect and read FLAC metadata

FLAC uses the very simple vorbis comment metadata format, which we can
now read most standard and non-standard fields from.

Userland/Libraries/LibAudio/VorbisComment.h

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2023, kleines Filmröllchen <filmroellchen@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/ByteBuffer.h>
+#include <LibAudio/LoaderError.h>
+#include <LibAudio/Metadata.h>
+
+namespace Audio {
+
+// https://www.xiph.org/vorbis/doc/v-comment.html
+ErrorOr<Metadata, LoaderError> load_vorbis_comment(ByteBuffer const& vorbis_comment);
+
+}