Use the stacktrace passed to Sentry.Event.transform_exception/2 when calling Exception.normalize/3

[potatosalad]

The stacktrace for certain errors (like FunctionClauseError) may resolve incorrectly inside Sentry.Event.transform_exception/2 due in part to the issue described in elixir-lang/elixir#7622.

To reproduce the issue, the following can be run to force a FunctionClauseError error report generated by a supervisor:

:error_logger.add_report_handler(Sentry.Logger)
{:ok, pid} = Task.Supervisor.start_link()
Task.Supervisor.start_child(pid, fn -> :lists.last([]) end)

In the generated event, the message will show:

(FunctionClauseError) no function clause matching in Keyword.delete_key/3

Instead of reporting as expected:

(FunctionClauseError) no function clause matching in :lists.last/1

[potatosalad]

It also appears that Exception.normalize/2 itself may be deprecated soon, which means that transforming an exception without a stacktrace may not be possible in the future: elixir-lang/elixir#7628

[mitchellhenke]

@potatosalad thank you so much for the detailed explanation and pull request! 💖 ❤️ 💜 💙