Implemented Android Demo Application for VoIP API

The app showcased the ability to send real-time voice data between two endpoints using the VoIP API.
Users can also configure session parameters such as the endpoint information and codec used.

Bug: webrtc:11723
Change-Id: I682f4aa743b707759536bce59e598789a77b7ec6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/178467
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Tim Na <natim@webrtc.org>
Commit-Queue: Tim Na <natim@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31775}

examples/BUILD.gn

@@ -27,6 +27,7 @@ group("examples") {
       ":AppRTCMobile",
       ":AppRTCMobile_test_apk",
       ":libwebrtc_unity",
+      "androidvoip",
     ]
 
     # TODO(sakal): We include some code from the tests. Remove this dependency