Client phase 3a: work with BugSplat to make Mac crash reporting more reliable

[nat-goodspeed]

When the Mac BugSplat client detects its host viewer is crashing, it writes state files to the local filesystem. The next time that viewer is run, the crash data captured in these files is sent to BugSplat.

The weak link there is that if the user is disgusted and never again runs that viewer, the crash goes unreported.

Embed, in the watchdog child process, the Mac BugSplat client. When the watchdog process detects that the viewer has terminated involuntarily, coax BugSplat to read the viewer's crash report files and send them right away.

This may require library enhancements from BugSplat.

Test Plan

Run the Mac viewer. Force a crash. Observe that the crash report is sent to BugSplat, even without running that viewer a second time.