ekf2: handle all time on delayed horizon (except for newest sample checks)

- a growing number of samples come into the backend with the time
already delayed (sensor's interrupt setting timestamp sample)
 - if the incoming timestamp is already delayed then the new data checks
(relative to latest IMU) can be slightly wrong
 - handle almost all timestamps and checks on delayed time horizon,
except for explicit checks of new samples
 - isRecent() and isTimedOut() helpers use delayed time
 - add new isNewestSampleRecent() used for checking the incoming
timestamp of the incoming (adjusted) data

src/modules/ekf2/EKF/ekf.h

@@ -477,7 +477,6 @@ private:
 	uint64_t _time_last_flow_terrain_fuse{0}; ///< time the last fusion of optical flow measurements for terrain estimation were performed (uSec)
 	uint64_t _time_last_beta_fuse{0};	///< time the last fusion of synthetic sideslip measurements were performed (uSec)
 	uint64_t _time_last_zero_velocity_fuse{0}; ///< last time of zero velocity update (uSec)
-	uint64_t _time_last_gps_yaw_data{0};	///< time the last GPS yaw measurement was available (uSec)
 	uint64_t _time_last_healthy_rng_data{0};
 	uint8_t _nb_gps_yaw_reset_available{0}; ///< remaining number of resets allowed before switching to another aiding source
 
@@ -581,7 +580,6 @@ private:
 	bool _gps_checks_passed{false};		///> true when all active GPS checks have passed
 
 	// Variables used to publish the WGS-84 location of the EKF local NED origin
-	uint64_t _last_gps_origin_time_us{0};	///< time the origin was last set (uSec)
 	float _gps_alt_ref{NAN};		///< WGS-84 height (m)
 
 	// Variables used by the initial filter alignment
@@ -1026,12 +1024,17 @@ private:
 
 	bool isTimedOut(uint64_t last_sensor_timestamp, uint64_t timeout_period) const
 	{
-		return last_sensor_timestamp + timeout_period < _time_last_imu;
+		return last_sensor_timestamp + timeout_period < _imu_sample_delayed.time_us;
 	}
 
 	bool isRecent(uint64_t sensor_timestamp, uint64_t acceptance_interval) const
 	{
-		return sensor_timestamp + acceptance_interval > _time_last_imu;
+		return sensor_timestamp + acceptance_interval > _imu_sample_delayed.time_us;
+	}
+
+	bool isNewestSampleRecent(uint64_t sensor_timestamp, uint64_t acceptance_interval) const
+	{
+		return sensor_timestamp + acceptance_interval > _newest_high_rate_imu_sample.time_us;
 	}
 
 	void startAirspeedFusion();