Add test utilities

Run ./out/<platform>/bin/test-self-view after building to run a simple
audio/video capture and output test.

Run ./out/<platform>/bin/test-send-receive after building to run a test
with one sender and one receiver in the same application.
And here for consistency both media session setters should either be (transfer none) or (transfer full). But not both different :) So you would be either leaking the payload here, or stealing the source from the caller.
I have them both as (transfer none)