Notebook Text Model Edit API debt

[rebornix]

Currently the NotebookTextModel has two sets of API

• applyEdits which applies edits from the extension host currently. It supports Undo/Redo.
• insertNewCell which handles cell insertion. It supports Undo/Redo.
• moveCellToIdx/removeCell handles edits from view model but doesn't handle Undo/Redo (managed by ViewModel)

We should use applyEdits only which handles edits from all sources (multi extension host and UI) and also handle Undo/Redo.

[jrieken]

@rebornix Came to the conclusion that replaceCells is enough to represent insert and remove but not "move", right?

[rebornix]

Didn't make decision yet if "move" should just a replace or stay what it is now.