new manual_control_switches msg (split out of manual_control_setpoint) (#16270)

- split out switches from manual_control_setpoint into new message manual_control_switches
 - manual_control_switches published at minimal rate (~ 1 Hz) or immediately on change
 - simple switch debounce in rc_update (2 consecutive identical decodes required)
 - manual_control_switches logged at full rate rather than sampled at (5-10% of messages logged)
 - manual_control_setpoint publish at minimal rate unless changing
 - commander handle landing gear switch for manual modes
 - processing of mode_slot and mode_switch is now split so we only do one or the other (not both)
     - a future step will be to finally drop mode_switch and accompanying switches entirely

Co-authored-by: Matthias Grob <maetugr@gmail.com>

src/modules/mc_pos_control/MulticopterPositionControl.hpp

@@ -135,7 +135,7 @@ private:
 	vehicle_control_mode_s	_control_mode{};		/**< vehicle control mode */
 	vehicle_local_position_s _local_pos{};			/**< vehicle local position */
 	home_position_s	_home_pos{};			/**< home position */
-	landing_gear_s _landing_gear{};
+
 	int8_t _old_landing_gear_position{landing_gear_s::GEAR_KEEP};
 
 	DEFINE_PARAMETERS(