MR discussion resolution introduces some surprising changes in discussions

Overall, the MR discussion resolution is pretty neat. There are a few things that continue to surprise me, though. I talked with @DouweM about this the other day. It seems like it's worth discussing to see if some improvements can be made.

1. Discussion no longer auto-resolve after changing that line of code. This is probably desired, as @DouweM mentioned, developers could simply change a line of code that had a discussion item on it and the discussion would collapse automatically, making it easy to miss.
2. Diffs don't update, which causes confusion after subsequent pushes. In this case you really can't trust the diff in the discussion at all. You would need to always switch over to diff view and scroll around to find the comment. And if you have happened to push since the comment was made, the discussion may not exist on the diff anymore. Example:

Looking forward to discussion on how we can improve this in future releases. Thanks!