Refactor writing MIDI events to buffers

This moves out the code from the carla plugin into the core, because
this code will be re-used for Lv2 MIDI handling soon.

include/MidiEventToByteSeq.h

@@ -0,0 +1,47 @@
+/*
+ * MidiEventToByteSeq.h - writeToByteSeq declaration
+ *
+ * Copyright (c) 2020-2020 Johannes Lorenz <jlsf2013$users.sourceforge.net, $=@>
+ *
+ * This file is part of LMMS - https://lmms.io
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program (see COPYING); if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301 USA.
+ *
+ */
+
+#ifndef MIDIEVENTTOBYTESEQ_H
+#define MIDIEVENTTOBYTESEQ_H
+
+#include <cstddef>
+#include <cstdint>
+
+#include "lmms_export.h"
+
+/**
+	Write MIDI event into byte sequence.
+
+	Conforming to http://lv2plug.in/ns/ext/midi#MidiEvent
+
+	@param data Pointer to the target buffer for the byte sequence. Must
+		point to existing memory with at least 3 bytes size.
+	@param bufsize Available size of the target buffer.
+	@return Used size of the target buffer, or 0 if the MidiEvent could not
+		be converted.
+*/
+std::size_t LMMS_EXPORT writeToByteSeq( const class MidiEvent& ev,
+										uint8_t* data, std::size_t bufsize );
+
+#endif // MIDIEVENTTOBYTESEQ_H