Support Mac Crash info

[Gankra]

This was just added to mozilla's minidump-stackwalk: mozilla-services/minidump-stackwalk#29

JSON Schema addition:

    "mac_crash_info" : {
       "num_records" : 2,
       "records" : [
          {
             "message" : "CryptKit fatal error: Raise test exception from _pthread_cond_wait(2)",
             "module" : "/System/Library/Frameworks/Security.framework/Versions/A/Security"
          },
          {
             "message" : "abort() called",
             "module" : "/usr/lib/system/libsystem_c.dylib"
          }
       ]
    },

The information is in a new MOZ_MACOS_CRASH_INFO_STREAM section.