title: in VsCode compeltion extention, how should I do to get the index when I accept a completion item?
body: <p>edit:</p>
  <p><a href="https://i.stack.imgur.com/AnGyJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AnGyJ.png" alt="like the picture shows" /></a>
  like the picture shows, I want to get the index of fouced item in the suggestion panel, here is 3.
  But I can't get this info from my custom <code>CompletionItem.command</code> arguments.</p>
  <p>If I got this, I could easily  figure out the Top-N whitch the user prefer to aceept my code suggestion</p>
  <hr />
  <p>I could tranfer the index of suggestions to it, but it is not correct When there are many suggestions. I mean the index you got is not the exeact index you see in the code completion widget.</p>