Describe the bug

When we have a flamegraph which profiled different threads separately (i.e. with the --threads option) and reverse it with jfrconv with --reverse, the per-thread stack traces will all be collapsed into e single stack trace.

Expected vs. actual behavior

The per-thread stack traces should be kept in the reversed graph. Notice that the --threads option for jfrconv only applies to JFR files and not to flamegraphs.

Reproduction Steps

1. Create a flamegraph with --threads
2. Reverse that flamegraph with jfrconv --reverse
3. In the reversed flamegraph, the stack traces won't be grouped by threads any more.

Additional Information/Context

No response

Async-profiler version

HEAD

Environment details

No response