[debugger] Use async fingerprints in finish controller.

The FinishThreadController previously did its own asynchronous search
for stack frames using IP/SP. This is moved to the asynchronous
fingerprint getter on the Stack which removes complexity from the finish
thread controller.

There should be no user-visible change.

TEST=unit

Change-Id: Id11ca7d3d06179bbb3b4ff42e6dac14a646a9336
5 files changed