Improving stdin line history: option to split line history per notebook

[telamonian]

Problem

Currently, the line history support for stdin input boxes (which pop up during eg an ipdb debugging session) is global for a single instance of jupyterlab. This is personally how I prefer line history to work, but I've gotten some feedback that it can be confusing for this history to not be split up for different notebooks.

Proposed Solution

Add an option that will segregate the stdin line history per notebook. This might be a little tricky to do, but I think it can be done relatively easily by making a few modifications to the data structure under which stdin line history is currently stored.

[krassowski]

Triage meeting notes: this may be good to be optional since some users may be used to status quo. Also, an option to have this per-environment could be nice.