go: encoding/json: add line number to SyntaxError

What version of Go are you using (go version)?

$ go version
go version go1.15.6 linux/amd64

Does this issue reproduce with the latest release?

Yes

What did you do?

package main

import (
	"encoding/json"
	"fmt"
	"io"
	"os"
)

func main() {
	dec := json.NewDecoder(os.Stdin)
	for {
		var m map[string]interface{}
		if err := dec.Decode(&m); err == io.EOF {
			break
		} else if err != nil {
			fmt.Printf("%#v\n", err)
			break
		}
	}
}

$ echo -e '{"x":\ny}' | go run jsonline.go 
&json.SyntaxError{msg:"invalid character 'y' looking for beginning of value", Offset:7}

At the moment SyntaxError provides an offset of the character that caused parsing error. The proposal is add the line number as well.

I could not find such an issue therefore opened this one, please close if it was already resolved.