Test: inline notebook diff view

[amunger]

Refs: #239635

• macOS @isidorn
• linux @justschen
• windows @bhavyaus

Complexity: 3

Authors: @amunger, @DonJayamanne

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1. add the setting "notebook.diff.experimental.toggleInline": true,
2. make changes to a notebook, either by
   a. making edits and then using the timeline to compare with previous snapshots or
   b. Use the SCM view and view the diff of unstaged changes
3. Use the editor menu in the top right to toggle the diff view to inline and ensure it works as expected
4. check adding/deleting cells as well as changing the content within a cell
   a. comparing both added/removed cells and modified cells at the same time doesn't always work well, but it should at least be comparable to the side-by-side view