Plane: ATT.DesPitch now reports actual target, not nav output (Float version)

[Georacer]

Alternative to #28991

It converts Plane::demanded_pitch_cd into a float, and can thus save a lot of headache: It is no longer necessary to have a second variable to track the value validity.

Still tested to work in SITL, by changing MANUAL->FBWA->MANUAL.

[peterbarker]

Suggested change

	// The instantaneous desired pitch angle. Hundredths of a degree.
	// The instantaneous desired pitch angle in degrees

[IamPete1]

There are some modes where we swap between angle controller and not. It does look like we currently just leave the angle targets hanging in those cases. Training is one case:

ardupilot/ArduPlane/mode_training.cpp

Lines 55 to 58 in 429ed5c

	if (plane.training_manual_pitch) {
	SRV_Channels::set_output_scaled(SRV_Channel::k_elevator, pexpo);
	} else {
	plane.stabilize_pitch();

Nav scripting is the other:

ardupilot/ArduPlane/Attitude.cpp

Lines 405 to 423 in 429ed5c

	} else if (nav_scripting_active()) {
	// scripting is in control of roll and pitch rates and throttle
	const float speed_scaler = get_speed_scaler();
	const float aileron = rollController.get_rate_out(nav_scripting.roll_rate_dps, speed_scaler);
	const float elevator = pitchController.get_rate_out(nav_scripting.pitch_rate_dps, speed_scaler);
	SRV_Channels::set_output_scaled(SRV_Channel::k_aileron, aileron);
	SRV_Channels::set_output_scaled(SRV_Channel::k_elevator, elevator);
	float rudder = 0;
	if (yawController.rate_control_enabled()) {
	rudder = nav_scripting.rudder_offset_pct * 45;
	if (nav_scripting.run_yaw_rate_controller) {
	rudder += yawController.get_rate_out(nav_scripting.yaw_rate_dps, speed_scaler, false);
	} else {
	yawController.reset_I();
	}
	}
	SRV_Channels::set_output_scaled(SRV_Channel::k_rudder, rudder);
	SRV_Channels::set_output_scaled(SRV_Channel::k_steering, rudder);
	SRV_Channels::set_output_scaled(SRV_Channel::k_throttle, plane.nav_scripting.throttle_pct);

It would be nice to reflect that in the log, but it is a existing issue, so it doesn't need to be resolved here.

[IamPete1]

I think this should be demanded_pitch_log, we need to make sure no one tries to use it for anything else. Should this be a logger.quiet_nanf()?

[IamPete1]

I think this also needs setting on 196 for the quadplane case. use_fw_attitude_controllers is not quite the same as show_vtol_view that we use for switching over logging, there maybe some overlap where this would be a change in behavior.