Native Editor - implement dirty tracking files for ipynb

[rchiodo]

In issue microsoft/vscode-python#7258 there are multiple options discussed. The ideal situation is option 4:

Option 4: Implement behavior similar to VSCode's auto-recover functionality that stores a dirty copy of what was edited and when VSCode is launched again, it displays that file as dirty. This is considerably more expensive than the other options here.

This issue is to make sure option 4 is implemented at some point.

[IanMatthewHuff]

I felt like I got it in a state once where it was asking me to save a file on close that I hadn't made dirty, but I was unable to get a repro on that with a bunch of trying. So validated.