Converge IMU faster at higher groundspeed during GPS Rescue (#12738)
* dynamic dcm_kp depending on groundspeed vs velocity to home
* reduce max pitch angle default to 40
* Only 10% of set velocity to home is enough, angle to 45
to reduce chance of sanity check against headwind
* fixes, thanks @KarateBrot
* Feedback from Ledvinap, ensure full pitch and yaw authority in descend
* pitch limit max of 1/3 and dcm_kp gain to 6x max
* apply IMU kP factor to yaw only via ez_ef
* More from @Ledvinap, constrain pitch in descent also
* Fix the velocity error gain, refactoring thanks to Ledvinap
* thanks, Mark!
* fixes, must be fabsf
* make IMU gain twice as sensitive to groundspeed error
* useCOG as float
* Fix unit test
* ensure cogYawGain is zero, except during gps rescue
* update comment after suggestion from ledvinap
* keep roll angle limit consistently at 50% of pitch limit when active
* changes to comments, thanks petr