Core coder and stereo DFT functions conversion/integration

[x] Use EVS version of GetTCXAvgTemporalFlatnessMeasure function with SUBBLOCK_NRG_CHANGE_E as exponent
[x] hq_hr_enc() conversion - some sub functions converted
[x] TNSAnalysis_ivas_fx function added
[x] stereo_tcx_core_enc: Lsf and Lsp related functions integrated
[x] stereo dft enc functions conversion