Summary: Code cleanup and creating a private decoder for error handler, since it can be triggered from in signal handler, where no lock can be taken
Reviewed-by: dholmes, kamg, acorn, coleenp

Summary: Made decoder thread-safe
Reviewed-by: coleenp, kamg

Reviewed-by: kvn, twisti, jrose
Contributed-by: NKurt Miller &lt;kurt@intricatesoftware.com&gt;, Greg Lewis &lt;glewis@eyesbeyond.com&gt;, Jung-uk Kim &lt;jkim@freebsd.org&gt;, Christos Zoulas &lt;christos@zoulas.com&gt;, Landon Fuller &lt;landonf@plausible.coop&gt;, The FreeBSD Foundation &lt;board@freebsdfoundation.org&gt;, Michael Franz &lt;mvfranz@gmail.com&gt;, Roger Hoover &lt;rhoover@apple.com&gt;, Alexander Strange <astrange@apple.com>

Summary: Implemented in-process C native stack frame decoding when symbols are available.
Reviewed-by: coleenp, never