Precision improvements to reduce high MLD issues

[x] Changes made in deindex_sph_idx_fx and ivas_dirac_dec_output_synthesis_process_subframe_psd_ls_fx to improve precision
[x] Improved precision for hStereoDft->smooth_res_nrg_fx and hStereoDft->smooth_dmx_nrg_fx buffers
[x] Added checks to prevent saturation for the buffers hHQ_core->old_out_fx and hHQ_core->old_out_LB_fx