Plane: postition control QPOS1 and QPOS2

[robertlong13]

Rebase of #21620 to 4.7dev

This doesn't work like it should. In the old PR, the comment

       // It never trys to speed up or slow down due to position error (unless in overshoot)

is correct. But now after rebasing to 4.7, it's not quite working that way. Something with the input shaping has changed and now the target position is lagging significantly behind the actual position, causing the aircraft to pitch way back, then pitch forward again (4.7dev does this too, which I'm trying to fix in another PR, but if this PR can achieve the same result, it has other benefits).

backtransition_21620_4.7dev.zip

I get the behavior I want if I use set_pos_vel_accel_NE_m instead of input_pos_vel_accel_NE_m on line 2603 but that's definitely not the right fix. Unfortunately, I don't understand the AC_PosControl library well enough. Hoping someone else sees something obvious here.