open method
The open() method of the MIDIPort interface makes the MIDI device
connected to this MIDIPort explicitly available.
If the port is successfully opened a new MIDIConnectionEvent is queued
to the MIDIPort.statechange_event and MIDIAccess.statechange_event
events, and the MIDIPort.connection property is changed to "open".
If the port is already open when this method is called, then the promise will resolve successfully.
Implementation
external JSPromise<MIDIPort> open();