intent to ship: change in signature generation for Java crashes

[William Kahn-Greene]

(cross-posted to stability, crash-reporting-wg)

Bug #1847429 covers a situation where Socorro (Mozilla's crash ingestion pipeline) is getting Java crash reports from Fenix users where there is a `JavaException` annotation value, but no `JavaStackTrace` annotation value. Signature generation uses the `JavaStackTrace` annotation data to generate stack traces for Java crash reports. Since there was no value, the crash reports would get the unhelpful signature "EMPTY: no frame data available".

https://bugzilla.mozilla.org/show_bug.cgi?id=1847429

This week, I plan to push a big change to signature generation which changes things to look for a `JavaStackTrace` annotation value and if that's not there, then look at the `JavaException` annotation value.

The change is implemented to minimally disrupt existing crash report signatures. It should only fix signatures for crash reports with "EMPTY: no frame data available" signatures. Further, I plan to reprocess crash reports with the bad signature since August 1st. At this time, there are around 50k crash reports.

Since this is currently a top crasher for Fenix, expect to see "EMPTY: no frame data available" mostly disappear and crash reports to show up in other signature buckets.

/will