Copter:fix bug in autotrim

[Hwurzburg]

This:

1. Fixes bugs in Copter: use Auxiliary function to control adjusting of AHRS trim from RC inputs #28881 (aux func was not init'd and auto trim not saved properly)
2. refactors to use an "allows_auto_trim" bool to avoid entering autotrim and then immediately cancelling; and neaten the code a bit
3. Adds Loiter/PosHold to autotrim for hands off trimming
4. Add a warning on attempting to enable autotrim when allowed, but not flying, rather than just entering and exiting immediately leaving a user to wonder why.
5. adjust marginally failing autotest

[rmackay9]

Hi @Hwurzburg, I'm not sure Loiter works though does it? I don't think it should work in Loiter..

[Hwurzburg]

Hi @Hwurzburg, I'm not sure Loiter works though does it? I don't think it should work in Loiter..

you are right....I got ahead of myself......removed the bool in Loiter.....will follow up with a modification that uses nav_controller->get_roll and pitch if in Loiter or PosHold modes instead of RC inputs in the auto_trim_run function....thanks for the catch....

[Hwurzburg]

@rmackay9 I found another bug and fixed it (was not properly saving trim and terminating auto_trim_run)
also got Loiter and Pos_hold working....checked sensitivities for using sticks or letting AP do it and they seem reasonable and unchanged