Allow scaled passthru to go to trim on rc failsafe

[Hwurzburg]

Allows selecting any scaled passthru channel to go to input trim on rc failsafe instead of freezing
Allows pilot controlled gimbals to revert to forward position while returning to home

builds off some of @peterbarker work

[IamPete1]

Do we need per channel options? Would one bit for all in RC_OPTIONS work?

[Hwurzburg]

Do we need per channel options? Would one bit for all in RC_OPTIONS work?

No...could have some pass thru things like airbrakes/slats...lights...etc that you want to stay unchanged while in fs also

[IamPete1]

Another option instead of a new parameter is to add another bunch of 16 scaled output functions for "RC in scaled trim in FS".

But I tend to think were getting a little too niche for most users and might be better just to say use scripting at this point. For example what if I want my scaled output to go to min or max on failsafe, should we add more parameters for that?

[Hwurzburg]

scripting is not available on many popular autopilots.....the F4 class is resurging with the new Chinese cpus also

[IamPete1]

I guess a alternative would be to still update rc in while in failsafe. Then you could set your failsafe positions in the transmitter and have them passed through.

[Hwurzburg]

Not a solution for rc failure failsafes...that is why we recommend using no pulses

[Hwurzburg]

SITL and board tested

[IamPete1]

Would fixing #24093 remove the need for this PR?

[Hwurzburg]

no...thats gimbal....and this PR actually stimulated that for the Gimbal library...this covers nonGimbal library applications...ie just a couple of servos which are pilot only controlled

[rmackay9]

In general this looks OK to me. I worry a little about scope creep going forward and the leak of failsafe actions out of the vehicle code and into the libraries.