External renderer unnecessary memory allocated

In the external renderer, module handles related to all possible functionalities are allocated regardless of whether the particular functionality is used or not. Consequently, unnecessary memory blocks are allocated for the majority of rendering test cases.

It concerns the following modules in IVAS_REND_Open():

• initHeadRotation()
• ivas_external_orientation_open()
• ivas_combined_orientation_open()
• isar_init_split_rend_handles()
• ivas_HRTF_statistics_init()

Finally, SPLIT_REND_WRAPPER splitRendWrapper within struct IVAS_REND should be defined dynamically only when needed.