o no longer toggles showing/hiding the output of a cell

[JasonWeill]

o no longer toggles showing/hiding the output of a cell, and I don't see any way to add this

Originally filed by @jph00 in #7041, referring to a regression from Jupyter Notebook 6 to 7.

[JasonWeill]

In nbclassic, based on Notebook 6, the o command takes a cell with output:

… and collapses the output:

[jtpio]

Maybe there could be a new command in JupyterLab for toggling the cell output, similar to the existing ones for collapsing and expanding the outputs:

That way the command would also be available in Notebook 7, and could be associated with a keyboard shortcut.