Refactor NetEq delay manager logic.

- Removes dependence on sequence number for calculating target delay.
- Changes target delay unit to milliseconds instead of number of
  packets.
- Moves acceleration/preemptive expand thresholds to decision logic.
  Tests for this will be added in a follow up cl.

Bug: webrtc:10333
Change-Id: If690aae4abf41ef1d9353f0ff01fb7d121cf8a26
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/186265
Commit-Queue: Jakob Ivarsson <jakobi@webrtc.org>
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32326}

modules/audio_coding/neteq/decision_logic_unittest.cc

@@ -43,6 +43,6 @@ TEST(DecisionLogic, CreateAndDestroy) {
   logic->SetSampleRate(fs_hz, output_size_samples);
 }
 
-// TODO(hlundin): Write more tests.
+// TODO(jakobi): Write more tests.
 
 }  // namespace webrtc