aaudio_loopback: improve tolerance to noise

Make silence detector less sensitive to noise by setting the
threshold proportional to the measured pulse level.

Make glitch detector less sensitive to noise by setting the
threshold proportional to the measured noise level.

Report signal to noise ratio.

Improved printed messages, show state as text.

Bug: 117834966
Test: aaudio_loopback -pl -tm
Change-Id: I5593cd1ade93ecbcb05f42af07626013d036f29a
Merged-In: I5593cd1ade93ecbcb05f42af07626013d036f29a