Some API deprecation -- ExperimentalAgc and ExperimentalNs are gone.
We're continuing to carry iSAC even though it's gone upstream, but maybe
we'll want to drop that soon.
This new lib contains the bare minimum to implement an iSAC encoder and
decoder.
The webrtc files have been copied from the revision as the existing
imported files (c8b569e0a7ad0b369e15f0197b3a558699ec8efa).
Corresponds to upstream commit 524e9b043e7e86fd72353b987c9d5f6a1ebf83e1
Update notes:
* Pull in third party license file
* Replace .gypi files with BUILD.gn to keep track of what changes
upstream
* Bunch of new filse pulled in as dependencies
* Won't build yet due to changes needed on top of these
