Fix "view as scrollable element" not working

[seeM]

The issue was due to cell output metadata being set to undefined by the Positron notebook controllers, causing the scrollable metadata to not be set here:

positron/src/vs/workbench/contrib/notebook/browser/view/renderers/backLayerWebView.ts

Lines 766 to 769 in 54d791d

	if (vm.model.metadata) {
	vm.model.metadata['scrollable'] = true;
	vm.resetRenderer();
	}

We now set metadata and also set outputType since it also makes life easier for the ipynb serializer:

positron/extensions/ipynb/src/serializers.ts

Line 182 in 3a8978a

switch (outputType) {

QA Notes

1. Run a Python notebook cell with the following code:

  # code with error
def divide_numbers(numbers):
    result = []
    for num in numbers:
        result.append(10 / num)
    return result

numbers_to_divide = [2, 4, 0, 5, 7]

try:
    divide_numbers(numbers_to_divide)
except Exception as e:
    error_message = f"Error: {e}\n" * 50  # Repeat error message
    raise RuntimeError(error_message)

2. Click "View as scrollable element" - it should work.
3. Also try the "Notebook: Toggle scrollable element" command with the cell selected.

[nstrayer]

Looks good and works for me.
Took me a while to figure out how adding the outputType field allowed scrollable to work but I get now that adding any metadata means that the metadata field is defined and can then me updated with new fields etc..