Detect line break in notebook cell content

[rebornix]

Issue Type: Bug

• Open a notebook which uses \n as line break on Windows
• Edit a cell, undo, save
• The document becomes dirty on SCM

What happens under the hood is now the cell is saved with \r\n.

VS Code version: Code - Insiders 1.57.0-insider (1e446df, 2021-06-01T05:13:48.346Z)
OS version: Windows_NT x64 10.0.19041

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-9700K CPU @ 3.60GHz (8 x 3600)
GPU Status	2d_canvas: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on oop_rasterization: enabled opengl: enabled_on rasterization: enabled skia_renderer: enabled_on video_decode: enabled vulkan: disabled_off webgl: enabled webgl2: enabled
Load (avg)	undefined
Memory (System)	31.93GB (17.22GB free)
Process Argv	--enable-proposed-api joyceerhl.vscode-pyolite --crash-reporter-id e73ca734-e67c-473d-8c47-80c5407fc859
Screen Reader	no
VM	0%

[vscode-triage-bot]

Pinging notebook topic followers: @claudiaregio @rchiodo @greazer @DonJayamanne @jilljac @IanMatthewHuff

[rebornix]

This is actually handled by the serializer (which gives the core value: string).