JSON crashlogs normally start with a single line of meta data that we
strip unconditionally. Some producers started omitting the meta data
which tripped up crashlog. Be more resilient by only removing the first
line when we know it really is meta data.
rdar://82641662
Add a parser for JSON crashlogs. The CrashLogParser now defers to either
the JSONCrashLogParser or the TextCrashLogParser. It first tries to
interpret the input as JSON, and if that fails falling back to the
textual parser.
Differential revision: https://reviews.llvm.org/D91130