Improve context of diff notes in discussion thread

Whenever leaving notes on a diff I like to begin discussion on a specific block of code from the top of that block, but when this diff note is in the discussion thread, it shows the line I've commented on, and a number of lines above that comment.

A lot of people have learned to deal with this by commenting on some arbitrary line below the beginning of the block, but I think we could improve the UX of this. I'm thinking either we show code on either side of the note, or if that isn't ideal, at very least, we should provide some sort of UI to the commenter that shows which lines will be included in the discussion comment.

The example below, there is a property that has a number of lines of code belonging to it. I am talking generally about this whole block of code, so I leave a comment on the line where the property is declared.

When changing to the discussion thread, I now have 10+ unrelated lines of code followed by my comment which talks about something completely beyond this diff snippet.

I had a quick google and it seems the only languages in which you read from the bottom up are ancient or related to magic in some way. 😝