Core coder and stereo path sub-functions conversion and integration

[x] Integration and conversion of core coder sub-functions:  acelp_core_enc, swb_pre_proc, swb_tbe_enc, ProcessIGF
[x] Stereo path functions conversion and integration: pre_proc_front_ivas, stereo_dft_enc_res_fx, stereo_dft_enc_write_bs_fx