Add ability to shift+click for multiple cell selection in the notebook

[ellisonbg]

In the classic notebook you can shift+click to select multiple cells. Add that to JupyterLab :)

[ellisonbg]

Plan:

• Add click handler to notebook/widget
• Add method to handle that event to notebook widget
• Test for shift (abort otherwise)
• Find selected cell and clicked cell.
• Import NotebookActions
• Call NotebookActions.extend... multiple times

[jasongrout]

multiple times

I think it might be better to make the extend function take a cell (or index), instead of rerunning its logic for every cell in between the active and clicked cells.

[blink1073]

or merge to an extendSelectionTo(index: number) function

[ellisonbg]

@spoorthyv any update on this one?

[spoorthyv]

I need some help with implementing an extendSelectionTo function. I was able to find the index of the target cell and pass that to the function, but I cant find a way to pass the index of the cell that is already selected.

[blink1073]

if you have the Notebook widget instance, you can call isSelected() on each cell.