Log non-strings into log file like console.log does

[mikiher]

This was inspired by #3398, in which the reporter attaches the log file, which doesn't contain a detailed logging of AggregateError.

Examining the Logger, I found that when logging to file and emiting log events to listeners, the log object is built like this:

    const logObj = {
      timestamp: this.timestamp,
      source: src,
      message: args.join(' '),
      levelName: this.getLogLevelString(level),
      level
    }

However, Array.join calls toString on each arg, which, in the case of Error args, just returns the name and message of the error, without the stack trace or any additional fields.

console.log on the other hand, uses util.inspect on non-string arguments, which returns a more detailed object representation, and also has special handling for Error objects.

I fixed this issue by mimicking how console.log builds the message.

I also made a couple of other minor changes:

• Moved the logging logic into a single private method \#log
• Before my changes, fatal and note always logged, regardless of this.logLevel, but file logging still checked against this.logLevel. I fixed the inconsistency (now file logging also disregards this.logLevel for fatal and note). I didn't know if I should also disregard it for log event emitting? currently left that unchanged.

In addition, I added unit tests for Logger.

[advplyr]

That makes sense. We can disregard those for the log event emitting also.

[mikiher]

I also needed to resolve a seemingly unrelated flakiness in the BookFinder unit test.

Not sure exactly what happened there. I modified the test code slightly and it went away (the many changes are due to prettier formatting).

[mikiher]

We can disregard those for the log event emitting also.

OK, I'll fix the code then.

[mikiher]

Done. This is ready for review.

[advplyr]

Thanks!