Core coder functions conversion and integration: acelp core, stereo tcx core [allow regression]

Few MLD differences are occurring after these changes. These are being checked, hence marking it [allow regression].

[x] acelp core sub-functions integration
[x] stereo dft res cod sub-functions
[x] stereo_tcx_core_enc sub-functions and cleanup
[x] TNSAnalysisStereo && enc_ste_pre_mdct integration
[x] sns_compute_scf_fx, ShapeSpectrum_ivas_fx, Quantize SNS in ivas_mdct_core_whitening_enc integration
[x] fd cng encode stack
[x] front_vad_fx() integration