Bug fix for changes introduced through MR455 for SynthesisSTFT

[x] Replaced extract_l with saturation functions to prevent wrap-around behavior.

EVS 26.444 BE test passes.
decoder pytests:
MLD scores:
Original inputs: 562 failed, 374 skipped
MLD > 10: 46
MLD > 5 : 108
MLD < 5 : 408
+10dB inputs: 562 failed, 374 skipped
MLD > 10: 168
MLD > 5 : 184
MLD < 5 : 210
-10dB inputs: 562 failed, 374 skipped
MLD > 10: 13
MLD > 5 : 48
MLD < 5 : 501

encoder pytests results:
MLD scores:
Original inputs: 562 tests:
MLD > 10: 16
MLD > 5 : 28
MLD < 5 : 518
+10dB inputs: 562 tests:
MLD > 10: 26
MLD > 5 : 75
MLD < 5 : 461
\-10dB inputs: 562 tests:
MLD > 10: 5
MLD > 5 : 19
MLD < 5 : 538