Fatal Handlers: Add an extension point to Fatal Handlers

Description:
When a Fatal Error occurs, we end up calling onFatalError from the signal handler which dumps the current ScopedTrackedObject of the thread that encountered a fatal error if there’s a related scope tracked object.

However, the current mechanism isn’t flexible enough -- for example it just dumps to std::cerr using output from the ScopedTrackedObject.

There are many cases where you might be interested in ingesting and transforming what’s dumped and where it’s dumped before we exit -- such as dumping in a particular format to be ingested by other systems, stripping away any PII, etc.

Let me know if this makes sense. Thanks!