Why don't you just use an external editor that supports this?
I second this request. It would be great to have a vertical panel of line numbers.
The internal editor displays line number in on the status bar.
Or are you asking for a panel with numbers of all visible lines?
Although there is a "Go to line" option in the internal file editor, it is a little bit tedious to use this each time, so would be nice to be able to have line numbers as an option in the Preferences.