TOC for .py files with percent markup

[syagev]

I suggest to have a TOC available for .py files with percent markup. I guess for that we'll need to have the user select which kind of "Outline" view is of interest - the one for regular code files (which will not pickup e.g. markdown cells), or the one adjusted for notebooks.

My use case - in our team we manage a big .py file that acts as a sort of "catalog" of useful and relatively independent cells. This has to go under source control for version management and collaboration. The typical workflow is then to open an Interactive Window and execute a few of the cells of interest. So for finding these cells in the large file the described TOC is useful.

Originally posted by @syagev in microsoft/vscode-jupyter#1348 (comment)

Also opened as issue under vscode-jupyter microsoft/vscode-jupyter#5552 since I'm not sure where the right place is.

[brettcannon]

Moved to #17218