get_indexed_fields
Description:
Fetches the ContactFields configured to be indexed, with thier respective BookIndexTypes.
Parameters:
| this | |
| types | A return location for the set of BookIndexTypes corresponding to each returned field, should be freed with g_free when no longer needed. | 
| n_fields | The number of elements in the returned arrays. | 
Returns:
| The array of indexed ContactFields. |