Clean up temperature msg fields (#24272)

* remove temp field from airspeed.msg, adjust temp selection

* temp-sensor hirarchy: airspeed, ext. baro, default value

* directly use diff-press or baro temp in true-airspeed  calc

* improve clarity

* add enum for temperature source in VehicleAirData.msg

msg/Airspeed.msg

@@ -5,6 +5,4 @@ float32 indicated_airspeed_m_s   # indicated airspeed in m/s
 
 float32 true_airspeed_m_s        # true filtered airspeed in m/s
 
-float32 air_temperature_celsius  # air temperature in degrees Celsius, -1000 if unknown
-
 float32 confidence               # confidence value from 0 to 1 for this sensor

msg/VehicleAirData.msg

@@ -6,10 +6,10 @@ uint64 timestamp_sample     # the timestamp of the raw data (microseconds)
 uint32 baro_device_id       # unique device ID for the selected barometer
 
 float32 baro_alt_meter			# Altitude above MSL calculated from temperature compensated baro sensor data using an ISA corrected for sea level pressure SENS_BARO_QNH.
-float32 baro_temp_celcius		# Temperature in degrees Celsius
 float32 baro_pressure_pa		# Absolute pressure in Pascals
+float32 ambient_temperature		# Abient temperature in degrees Celsius
+uint8 temperature_source		# Source of temperature data: 0: Default Temperature (15°C), 1: External Baro, 2: Airspeed
 
 float32 rho				# air density
-float32 eas2tas         # equivalent airspeed to true airspeed conversion factor
 
 uint8 calibration_count     # Calibration changed counter. Monotonically increases whenever calibration changes.