Plane: added Q_FW_LND_ANGLE

[tridge]

this controls the acceptance angle of the track towards the center of the circle for a spiral descent VTOL landing. Reducing this value from the default of 30 may be useful in some vehicles to get a neater landing approach

[Hwurzburg]

you wouldnt have a screen shot of a GCS path showing this effect would you? for the wiki

[IamPete1]

If we can avoid a param and adjust the hard coded value I think that would be better. The stopping distance is always used, if the mode switch is already happening as the acceptance angle is reached lowering it will delay that mode switch. So it will likely result in a overshoot, although this may still be neater than what we do now. If the radius is large then this threshold angle change will have little effect.

[IamPete1]

@Hwurzburg For a spiral and transition into the wind VTOL landing (Q_RTL_MODE 2) this changes the angle at which the vehicle will switch from RTL to QRTL.