Copy external/abseil-cpp into webrtc to update to version 20211102.0
to pick up changes that fix compiling against musl libc.
Bug: 190084016
Test: m USE_HOST_MUSL=true host-native
Test: m checkbuild
Change-Id: I0ab600cd8db93a55eda8358cdbecd21c2f78d8fb
Renamed abseil modules to make them webrtc specific.
Restricted visibility of abseil modules to webrtc packages.
Bug: 171836454
Test: Builds
Change-Id: Icf24c7e3093a77dd9a26e7ec78bd531eb1ad3dec