AP_ExternalAHRS: Added Advanced Navigation Device Support

EAHRS_TYPE: 3 (AdNav) has been added to the AP_External_AHRS.h/.cpp files.
New Class AP_ExternalAHRS_AdvancedNavigation added in new .cpp/.h files.
Supports any Advanced Navigation Packet Protocol (ANPP) device with different devices having slight behaviour changes.

libraries/AP_ExternalAHRS/AP_ExternalAHRS.cpp

@@ -24,6 +24,7 @@
 #include "AP_ExternalAHRS_backend.h"
 #include "AP_ExternalAHRS_VectorNav.h"
 #include "AP_ExternalAHRS_MicroStrain5.h"
+#include "AP_ExternalAHRS_AdvancedNavigation.h"
 
 #include <GCS_MAVLink/GCS.h>
 
@@ -102,6 +103,11 @@ void AP_ExternalAHRS::init(void)
     case DevType::MicroStrain5:
         backend = new AP_ExternalAHRS_MicroStrain5(this, state);
         return;
+#endif
+#if AP_EXTERNAL_AHRS_ADNAV_ENABLED
+    case DevType::AdNav:
+        backend = new AP_ExternalAHRS_AdvancedNavigation(this, state);
+        break;
 #endif
     }
 

libraries/AP_ExternalAHRS/AP_ExternalAHRS.h

@@ -49,7 +49,9 @@ class AP_ExternalAHRS {
 #if AP_EXTERNAL_AHRS_MICROSTRAIN5_ENABLED
         MicroStrain5 = 2,
 #endif
-        // 3 reserved for AdNav
+#if AP_EXTERNAL_AHRS_ADNAV_ENABLED
+        AdNav = 3,
+#endif
         // 4 reserved for CINS
         // 5 reserved for InertialLabs
         // 6 reserved for Trimble