TrackPanelAx: add Navigate function for NVDA object navigation

accNavigate is deprecated, but NVDA uses it for object navigation. (Jaws and narrator do not).
So add Navigate function to TrackPanelAx.

Info on accNavigate:
https://msdn.microsoft.com/en-us/library/windows/desktop/dd318473(v=vs.85).aspx

src/TrackPanelAx.cpp

@@ -642,4 +642,63 @@ wxAccStatus TrackPanelAx::GetFocus( int *childId, wxAccessible **child )
 #endif
 }
 
+// Navigates from fromId to toId/toObject
+wxAccStatus TrackPanelAx::Navigate(wxNavDir navDir, int fromId, int* toId, wxAccessible** toObject)
+{
+   int childCount;
+   GetChildCount( &childCount );
+
+   if (fromId > childCount)
+      return wxACC_FAIL;
+
+   switch (navDir) {
+   case wxNAVDIR_FIRSTCHILD:
+      if (fromId == CHILDID_SELF && childCount > 0 )
+         *toId = 1;
+      else
+         return wxACC_FALSE;
+      break;
+
+   case wxNAVDIR_LASTCHILD:
+      if (fromId == CHILDID_SELF && childCount > 0 )
+         *toId = childCount;
+      else
+         return wxACC_FALSE;
+      break;
+
+   case wxNAVDIR_NEXT:
+   case wxNAVDIR_DOWN:
+      if (fromId != CHILDID_SELF) {
+         *toId = fromId + 1;
+         if (*toId > childCount)
+            return wxACC_FALSE;
+      }
+      else
+         return wxACC_NOT_IMPLEMENTED;
+      break;
+
+   case wxNAVDIR_PREVIOUS:
+   case wxNAVDIR_UP:
+      if (fromId != CHILDID_SELF) {
+         *toId = fromId - 1;
+         if (*toId < 1)
+            return wxACC_FALSE;
+      }
+      else
+         return wxACC_NOT_IMPLEMENTED;
+      break;
+
+   case wxNAVDIR_LEFT:
+   case wxNAVDIR_RIGHT:
+      if (fromId != CHILDID_SELF)
+         return wxACC_FALSE;
+      else
+         return wxACC_NOT_IMPLEMENTED;
+      break;
+   }
+
+   *toObject = nullptr;
+   return wxACC_OK;
+}
+
 #endif // wxUSE_ACCESSIBILITY

src/TrackPanelAx.h

@@ -104,6 +104,9 @@ public:
    // Returns a localized string representing the value for the object
    // or child.
    wxAccStatus GetValue(int childId, wxString* strValue) override;
+
+   // Navigates from fromId to toId/toObject
+   wxAccStatus Navigate(wxNavDir navDir, int fromId, int* toId, wxAccessible** toObject) override;
 #endif
 
 private: