When multiple panics occur at the same time (usually because one thread
panics, and another thread joins it), multiple panic JSON objects can
get written to the same panic file. The resulting file won't be valid
JSON.
This PR addresses that problem via two changes:
* Format panic files as single-line JSON objects
* When a panic file isn't valid JSON, try taking the first line
In the future, we could try combining all of the backtraces, but for
now, I just want to avoid a problem of not reporting a panic at all.
Release Notes:
- Fixed a problem with Zed's internal crash reporting.
Max Brunsfeld
8592208d3a