Copter: Support HexaDecaOcta (OCTA-X16)

[muramura]

Feature request

Is your feature request related to a problem? Please describe.

I want to support HexaDecaOcta (OCTA-X16).
I need 16 MOTORs.
ArduPilot has a maximum of 12.
The "flying car" being promoted in Japan is the HexaDecaOcta (OCTA-X16).

https://youtu.be/_tWrx7TdJ10

This vehicle will incorporate safety features in the future.
We believe that incorporating this safety functionality can be used as an unmanned aircraft multicopter.

Describe the solution you'd like

I would increase the number of motors from 12 to 16.
I have PIXHAWK 5x and 6x with 8 MAIN and 8 AUX.
I believe I can achieve OCTA-X16 with this FC.

I do not know the servo allocation for motors 13-16.
I would like a hint.

Describe alternatives you've considered

None

Platform
[ ] All
[ ] AntennaTracker
[X] Copter
[ ] Plane
[ ] Rover
[ ] Submarine

Additional context

[muramura]

I would add HEXADECAOCTA based on DODECAHEXA.
I add the definition of HEXADECA rotor to MAVLINK.

The motor table is shown in the image.

[muramura]

@rmackay9 san

I added the code for HexadecaOcta (OCTA-X16).
I would like to know if this code check is ok.
In SITL, the servo values changed.
But I can't simulate it correctly.

https://github.com/muramura/ardupilot/tree/AP_Support_HexadecaOcta_OCTA_X16