Confusing source code position in error message

[zhongl]

Input

```scala mdoc
extension (x: Int)
    def ===(y: Int) = x == y

1 === ""

    1 === 1    

### Command line

coursier launch org.scalameta:mdoc_3:2.5.3

### Output

extension (x: Int)
    def ===(y: Int) = x == y

1 === ""
// error:
// Found:    ("" : String)
// Required: Int
//     1 === 1
//          ^

    1 === 1

Source code position above

// 1 === 1 // ^

suppose to be 

// 1 === "" // ^^

[zhongl]

https://github.com/scalameta/mdoc/blob/06c90343cb66265e818da7fcb3ccd9ff46b9849d/mdoc/src/main/scala/mdoc/internal/markdown/Renderer.scala#L151-L155

I think TokenEditDistance from doc.sections cause confusing source code position.

I'd like to submit a PR to fix it, if it make sense.

[tgodzik]

Go ahead! I haven't had the chance to look at the issue yet.