Add CopyWith to LogRecord

[SharbelOkzan]

Consider the following use-case

Logger.root.onRecord.listen(logToCosole);
Logger.root.onRecord.listen(CrashAnlyticsTool.listenToLogs);

Where:
logToConsole is my custom function that logs to the debug console.
CrashAnlyticsTool is an external library, compatible with the logging package and provides a method listenToLogs via an extension. (a real example can be sentry_logging.

Now say that I decided to add a warning emoji (⚠️) to the logs of level SEVER. I can modify logToConsole to add the emoji on the fly before dumping to the console. However, I'm not able to modify the external method CrashAnlyticsTool.listenToLogs.
Using stream.map is one good solution. The problem is that LogRecord is immutable, doesn't have copyWith method, and doesn't have a constructor that exposes all fields.

The proposed change is either:

1. Adding a copyWith method
2. Adding a named constructor that accepts time and sequenceNumber as params.

Then the solution for the above will look somthing like

  LogRecord converter(LogRecord event) {
    return event.copyWith(message: "⚠️" + event.message);
  }
  Logger.root.onRecord.map(converter);
  Logger.root.onRecord.listen(logToCosole);
  Logger.root.onRecord.listen(CrashAnlyticsTool.listenToLogs);