This change cuts across LLVM and compiler-rt to add support for
rendering custom events in the XRayRecord type, to allow for including
user-provided annotations in the output YAML (as raw bytes).
This work enables us to add custom event and typed event records into
the llvm::xray::Trace type for user-provided events. This can then be
programmatically handled through the C++ API and can be included in some
of the tooling as well. For now we support printing the raw data we
encounter in the custom events in the converted output.
Future work will allow us to start interpreting these custom and typed
events through a yet-to-be-defined API for extending the trace analysis