AP_GPS: understand uBlox fix_type of 4 as being GNSS and dead reckoning

[peterbarker]

Closes https://github.com/ArduPilot/ardupilot/issues/27632

This L series seems to be able to suck sensor data in to provide an inertial solution.

I'm actually a little concerned about feeding this estimate into our EKF. Wouldn't the EKF's solution end up with measured acceleration applied twice, once from ArduPilot's sensors, once by whatever is feeding the GPS unit?

[peterbarker]

Board                    AP_Periph  blimp  bootloader  copter  heli  iofirmware  plane  rover  sub
CubeOrange-periph-heavy  -48                                                                   
Durandal                            -48    *           -48     -48               -48    -48    -48
Hitec-Airspeed           *                                                                     
KakuteH7-bdshot                     -48    *           -48     -48               -48    -48    -48
MatekF405                           -56    *           -56     -56               -56    -56    -56
Pixhawk1-1M-bdshot                  -56                -56     -56               -56    -56    -56
f103-QiotekPeriph        *                                                                     
f303-Universal           -48                                                                   
iomcu                                                                *                         
revo-mini                           -56    *           -56     -56               -56    -56    -56
skyviper-v2450                                         -56                                     

[tridge]

let's try and get a flight log and look at the innovations, preferably with some movement, so CIRCLE mode, or some significant flight under pilot control

[MallikarjunSE]

It could be using this. https://www.u-blox.com/en/product/ubx-m9140-ka-dr-chip Recent DJI drones use this which has built in IMU.