Confusing notebook diff with line break change only

[rebornix]

Imagine if we have a github issue notebook, which contains multi-line queries with mixed line breaks (a mix of \r\n and \n), and the preferred/detected line break is \n:

• replace one of the \r\n with \n
• there is now a change in SCM
• open the file in notebook diff editor
• there is no change at all visually

There are two issues here

• firstly, we normalize the line breaks in text model so the diff editor is correct, there is no difference between the original and modified text model. tracking issue Provide option to opt out of line ending normalisation for files #127
• secondly, even if we don't normalize the line breaks, we don't show line break changes in diff editor.

[rebornix]

The second is also a dup of #19254