Add Cancel button for commenting and other comment feature improvements

The new comment feature is very poorly designed

1. There’s no Cancel button after you enter something, and you can’t even press ESC to cancel it. If you do so, the comment dialog will wiggle and doesn’t give any feedback explaining why, which is very annoying. You have to clear the input field first, and then press ESC to cancel a comment.

2. The “emoji” and “@” icons don’t show up by default. They only show up after you input something. It doesn’t make sense.
   

   

3. All comments are displayed by default now, no matter you’re on comment mode or not, and you have to press “shift+c” to hide it. Maybe for some teams commenting is very essential, but it’s too much making it default to me personally.