This CL adds new fuzzer tests for the DecodeRedundant and
IncomingPacket methods of AudioDecoder. In practice, only Opus has
DecodeRedundant, and only iSAC has IncomingPacket. Did some minor work
to generalize the helper function reading values from the fuzzed
input.
BUG=webrtc:5306
R=pbos@webrtc.org
NOTRY=true
Review URL: https://codereview.webrtc.org/1607173003
Cr-Commit-Position: refs/heads/master@{#11533}