LoudnessEnhancer audio effect implementation

Implementation based on DRC effect, controlled by a
 target gain.
 The target gain is used to amplify the signal at
 the input of the DRC, and to compute the knee
 of the DRC.

Bug 8413913

Change-Id: I386d64793a9fa3f7218e053d6f0a99f6836c02bd
19 files changed