Explore option for allowing to run all cells in a folded markdown region

[miguelsolorio]

Separating this out from #132690

When a markdown cell has code cells folded underneath, the suggestions is to surface the total number of cells folded and to show a run action next to it:

Running the cell would show progress for the cells (with a stop action that will interrupt the kernel). And when the cell is finished, the cell returns the previous state. You can also click on the cell ... to expand the collapsed state (which is equivalent to opening the folded markdown region)