VTOL rate control architecture improvements (#10819)

* attitude and rate setpoint message: use 3D array for thrust demand
* FixedWingAttitudeControl: rework airspeed scaling
  * move airspeed and scaling calculation into separate method
  * if vtol in hover and airspeed disabled use minimum airspeed instead of trim airspeed

msg/vehicle_attitude_setpoint.msg

@@ -12,7 +12,9 @@ float32 yaw_sp_move_rate	# rad/s (commanded by user)
 float32[4] q_d			# Desired quaternion for quaternion control
 bool q_d_valid			# Set to true if quaternion vector is valid
 
-float32 thrust			# Thrust in Newton the power system should generate
+# For clarification: For multicopters thrust_body[0] and thrust[1] are usually 0 and thrust[2] is the negative throttle demand.
+# For fixed wings thrust_x is the throttle demand and thrust_y, thrust_z will usually be zero.
+float32[3] thrust_body		# Normalized thrust command in body NED frame [-1,1]
 
 bool roll_reset_integral	# Reset roll integral part (navigation logic change)
 bool pitch_reset_integral	# Reset pitch integral part (navigation logic change)

msg/vehicle_rates_setpoint.msg

@@ -3,6 +3,7 @@ uint64 timestamp	# time since system start (microseconds)
 float32 roll		# body angular rates in NED frame
 float32 pitch		# body angular rates in NED frame
 float32 yaw		# body angular rates in NED frame
-float32 thrust		# thrust normalized to 0..1
 
-# TOPICS vehicle_rates_setpoint mc_virtual_rates_setpoint fw_virtual_rates_setpoint
+# For clarification: For multicopters thrust_body[0] and thrust[1] are usually 0 and thrust[2] is the negative throttle demand.
+# For fixed wings thrust_x is the throttle demand and thrust_y, thrust_z will usually be zero.
+float32[3] thrust_body	# Normalized thrust command in body NED frame [-1,1]