AP_NavEKF3: Add accessor function for yaw alignment status

libraries/AP_NavEKF3/AP_NavEKF3.cpp

@@ -2022,3 +2022,12 @@ void NavEKF3::writeDefaultAirSpeed(float airspeed, float uncertainty)
         }
     }
 }
+
+// returns true when the yaw angle has been aligned
+bool NavEKF3::yawAlignmentComplete(void) const
+{
+    if (!core) {
+        return false;
+    }
+    return core[primary].have_aligned_yaw();
+}

libraries/AP_NavEKF3/AP_NavEKF3.h

@@ -373,6 +373,9 @@ public:
     // parameter conversion
     void convert_parameters();
 
+    // returns true when the yaw angle has been aligned
+    bool yawAlignmentComplete(void) const;
+
 private:
     uint8_t num_cores; // number of allocated cores
     uint8_t primary;   // current primary core