USB MIDI: Multijack MIDI 1.0 for MIDI 2.0 devices

MIDI 2.0 devices only show one input and output port for its backup
MIDI 1.0 path. This CL reads the jack counts and creates encoders
and decoders accordingly.

UsbMidiPacketConverter has been refactored to use cable numbers for
multiplexing USB MIDI streams.

Bug: 266473128
Test: MidiScope/MidiKeyboard on multiport MIDI device
Test: UmpMidiScope on MIDI 2.0 devices
Change-Id: I58799393ab0bddf7c6a6c63f1ab014accf1ab10e