Harmonize extend_frm_*fx() and shrink_frm_*fx()

Bug description

The function pairs

• extend_frm_fx() and extend_frm_ivas_fx()
• shrink_frm_fx() and shrink_frm_ivas_fx()

are almost identical (except from one scaling + isSilence_ivas_fx() vs. isSilence_fx()) - it should be feasible to harmonize them.