nativemidi: Prototype demonstrating native access to IMidiDeviceServer

Framework changes and a demo app
Comment and finalized Native MIDI API
Replaced fixed PortRegistry tables with std::map.
more error handling.
Removed not-very-useful MidiDeviceManager class.
Made Java API functions @hide.

Bug: 30252756

Test: Manual
Change-Id: Iae98e589f38ef6d625ff0842401193fe98c5d881