Import abseil-cpp to third_party

Renamed abseil modules to make them webrtc specific.
Restricted visibility of abseil modules to webrtc packages.

Bug: 171836454
Test: Builds

Change-Id: Icf24c7e3093a77dd9a26e7ec78bd531eb1ad3dec
diff --git a/Android.bp b/Android.bp
index 825e183..9f90f09 100644
--- a/Android.bp
+++ b/Android.bp
@@ -25,7 +25,7 @@
         "-DWEBRTC_LINUX",
     ],
     header_libs: [
-        "libabsl_headers",
+        "libwebrtc_absl_headers",
     ],
     static_libs: [
         "libaom",