MLD improvements through precision changes, exponent usage correction and saturation fixes

[x] Fixed a condition check in core_switching_post_dec_ivas_fx
[x] Fix for ltv-decorr saturation issue
[x] Precision improvement for reference_power in protoSignalComputation2_fx
[x] Fix: Calling decoder_tcx_post_ivas_fx instead of decoder_tcx_post_fx in stereo_tcx_core_dec_fx
[x] Fix for wrong exponent usage for mixing_matrix_old_fx and mixing_matrix_res_old_fx buffers during bitrate switching

• EVS 26.444 BE test passes.
• decoder pytests:
  MLD scores:
  Original inputs: 562 failed, 374 skipped
  MLD > 10: 2
  MLD > 5 : 17
  MLD < 5 : 543
  +10dB inputs: 562 failed, 374 skipped
  MLD > 10: 38
  MLD > 5 : 110
  MLD < 5 : 414
  -10dB inputs: 562 failed, 374 skipped
  MLD > 10: 0
  MLD > 5 : 5
  MLD < 5 : 557
• encoder pytests results:
  MLD scores:
  Original inputs: 562 tests:
  MLD > 10: 18
  MLD > 5 : 67
  MLD < 5 : 477
  +10dB inputs: 562 tests:
  MLD > 10: 69
  MLD > 5 : 122
  MLD < 5 : 371
  -10dB inputs: 562 tests:
  MLD > 10: 5
  MLD > 5 : 24
  MLD < 5 : 533