Add files to __init__ for autocomplete in VS Code

[hoxbro]

When writing in vs code the autocomplete only works for modules imported in an __init__.py file, e.g. pn.widgets.IntSlider work but pn.viewable.Viewer does not. See here:

example.1.mp4

The solution is pretty easy as .viewable only needs to be added to the __init__.

example.2.mp4

I don't know if #3132 will fix this. When you have time @MarcSkovMadsen can you check this?

[MarcSkovMadsen]

I don't expect #3132 to fix it.