This CL adds the GainCurveApplier (GCA). It owns a FixedDigitalLevelEstimator (LE) and an InterpolatedGainCurve (IGC). The GCA uses the LE to compute the input signal level, looks up a gain from IGC and applies it on the signal. The other IGC and LE submodules were added in previous CLs [1] and [2]. This CL also turns on AGC2 in the APM fuzzer. [1] https://webrtc-review.googlesource.com/c/src/+/51920 [2] https://webrtc-review.googlesource.com/c/src/+/52381 Bug: webrtc:7949 Change-Id: Idb10cc3ca9d6d2e4ac5824cc3391ed8aa680f6cd Reviewed-on: https://webrtc-review.googlesource.com/54361 Commit-Queue: Alex Loiko <aleloi@webrtc.org> Reviewed-by: Sam Zackrisson <saza@webrtc.org> Cr-Commit-Position: refs/heads/master@{#22103}