AP_NavEKF3: add accessor for GSF yaw estimator

libraries/AP_NavEKF3/AP_NavEKF3.cpp

@@ -2015,3 +2015,12 @@ bool NavEKF3::isVibrationAffected(int8_t instance) const
     }
     return false;
 }
+
+// get a yaw estimator instance
+const EKFGSF_yaw *NavEKF3::get_yawEstimator(void) const
+{
+    if (core) {
+        return core[primary].get_yawEstimator();
+    }
+    return nullptr;
+}

libraries/AP_NavEKF3/AP_NavEKF3.h

@@ -27,6 +27,7 @@
 #include <AP_NavEKF/AP_NavEKF_Source.h>
 
 class NavEKF3_core;
+class EKFGSF_yaw;
 
 class NavEKF3 {
     friend class NavEKF3_core;
@@ -358,6 +359,9 @@ public:
     // if instance < 0, the primary instance will be used
     bool isVibrationAffected(int8_t instance) const;
 
+    // get a yaw estimator instance
+    const EKFGSF_yaw *get_yawEstimator(void) const;
+
 private:
     uint8_t num_cores; // number of allocated cores
     uint8_t primary;   // current primary core

libraries/AP_NavEKF3/AP_NavEKF3_core.h

@@ -421,6 +421,9 @@ public:
     // returns true when the state estimates are significantly degraded by vibration
     bool isVibrationAffected() const { return badIMUdata; }
 
+    // get a yaw estimator instance
+    const EKFGSF_yaw *get_yawEstimator(void) const { return yawEstimator; }
+
 private:
     EKFGSF_yaw *yawEstimator;
     AP_DAL &dal;