This PR take up #12455 and #12626 (mission yawing timeout) and should improve the user experience/safety of VTOL forward transitions in mission mode. It only affects both VTOL_TAKEOFF and VTOL_TRANSITION commands.

Issues

1. Before a VTOL_TRANSITION to fixed-wing, the heading needs to be aligned to the next waypoint, otherwise it won't start transitioning. This is a problem when weather vane (WV) is active, as then the heading is always aligned against the wind. Currently the transition thus does not happen with cross/tail wind.

2. Mission yawing timeout in mission not working #12626 (mission yawing timeout)
   Even with WV disabled, when flying with high cross/tail winds, the aerodynamic passive yaw stability always yaws the VTOL into the wind. If this effect is bigger than the maximum yaw control authority, then yaw setpoints can't be followed. This can then be a problem if a transition is not planned against the wind. In this case, if the vehicle can't reach the transition heading, the mission should be aborted and RTL. The time the vehicle has max time to reach transition heading is set with MIS_YAW_TMT (a negative value disables this timeout). Currently this timeout does not work, so keeps trying indefinitely to reach the heading.

3. The direction of the front transition at a VTOL_TAKEOFF waypoint (this waypoint is the one that per default gets selected for the first waypoint of a VTOL mission) is currently in an arbitrary direction with weather vane enabled (resp. the heading from takeoff is kept if weather vane is disabled).

Changes

1. This PR disables the WV during a VTOL_TRANSITION (to fixed-wing) as soon as the transition altitude is reached and the aligning phase starts. WV stays enabled (if WV_EN params is set to 1) for all other hover flight phases.
2. Fixed yawing timeout in navigator (timer was wrongly reset all the time).
3. Set the heading of the front transition of a VTOL_TAKEOFF to this VTOL_TAKEOFF waypoint. This heading is then enforced, meaning that like with a normal VTOL_TRANSITION wp, it won't do the transition if the aligning times out (controlled with MIS_YAW_TMT).

Follow-up issues to solve

• explain in QGC that for a VTOL_TAKEOFF, the direction of the transition is towards this waypoint and that it should be placed some distance from home and in the direction where one wants the transition to happen (it has to be accepted in FW mode and thus the vehicle will in worst case turn back to fly through it if it is too close to home)
• give the user the possibility to set the direction of a VTOL_TAKEOFF to e.g. a fixed heading, or to discard any heading setpoint and just transition (e.g. into wind if WV is enabled). (see MAV_CMD_NAV_VTOL_TAKEOFF: Heading not considered #12660)