zapslog: Apply callerSkip when addCaller

[sjones4]

CallerSkip was added to the Handler but only used for the stacktrace, it should also be applied to the caller with an appropriate offset.

Currently the stacktrace can be correct for a wrapped logger but there is no way to fix the caller information.

Here is the equivalent logger functionality where the skip is applied for the caller:

zap/logger.go

Lines 393 to 414 in c17272e

	stack := stacktrace.Capture(log.callerSkip+callerSkipOffset, stackDepth)
	defer stack.Free()
	if stack.Count() == 0 {
	if log.addCaller {
	fmt.Fprintf(log.errorOutput, "%v Logger.check error: failed to get caller\n", ent.Time.UTC())
	_ = log.errorOutput.Sync()
	}
	return ce
	}
	frame, more := stack.Next()
	if log.addCaller {
	ce.Caller = zapcore.EntryCaller{
	Defined: frame.PC != 0,
	PC: frame.PC,
	File: frame.File,
	Line: frame.Line,
	Function: frame.Function,
	}
	}

[CLAassistant]

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