ivas_front_vad_spar() functions/sub funcs, stereo mdct stereo enc funcs

[x] Converted/Integrated the following functions and its sub functions in ivas_front_vad_spar():
noise_est_down(), correlation_shift(), dtx(), find_wsp(), StableHighPitchDetect(), multi_harm(), vad_param_updt(), ivas_smc_gmm(), ivas_long_enr()
[x] In stereo mdct stereo encoder module, following functions are ported to fixed point:
RCcontextMapping_encode2_estimate_bandWise, RCcontextMapping_encode2_estimate_bandWise_start, RCcontextMapping_encode2_estimate_no_mem_s17_LCS, find_last_nz_pair, IGFEncStereoEncoder, IGF_MsStereoDecision, calcCoh, FindSplitRatio, GetChannelEnergyRatio, MsStereoDecision, QuantSpecEstimateBits, SQ_gain_estimate_stereo, context_update, convertToBwMS, convertToMS, dft_ana_init, initMdctItdHandling, initMdctStereoEncData, ms_inv_mask_processing, ms_processing, stereo_coder_tcx, stereo_mdct_enc_destroy, write_itd_data, write_stereo_to_bitstream, tcx_scalar_quantization