to allow descending by stick for reliable land detection.
Issue:
Stick smoothing gets completely reset to state when not taken off
-> downwards velocity setpoint is gone when not taken off
-> in_descend flag of land detection is never true when not taken off
-> when landing but falling out of landing it landing detection fails
bafore taking off and landing again
This was only handled outside because FlightTaks lived in the
multicopter position controller which produces the data that was
needed but now it doesn't make sense anymore to handle this
subscription separately.
It's better to have it inside the base task to have the data available
on task activation sucht that e.g. Altitude mode can take over smoothly
from Position mode.
It is important that setpoints get initialized with NAN and not overwritten
if specifically set by a successful flight task execution. It's then
clear if any setpoints were intentionally and successfully set.
Crucial for the position controller's emergency failsafe and the
seamless setpoint handover to the next flight task.
