SF: Add continuous transaction tracing

Add the ability to capture all incoming transactions into a ring
buffer. Capture transactions as the come in through the binder
thread. On the main thread push committed transactions to the
tracing thread which will then add to the buffer and purge
older entries as the buffer gets filled.

Also introduce a new flag to enable transaction tracing (disabled
by default).

Test: presubmit
Bug: 200284593

Change-Id: I90dd0fa4f89f68cfc7b7922ecd0bba4adab8d7a4