Add folding / unfolding for extension packs in the Extensions view

[mpekurin]

It would be nice if vscode has used a foldable tree view for extension packs in the Extensions view. E. g. instead of

Jupyter Keymap
isort
Jupyter
Jupyter Cell Tags
Jupyter Notebook Renderers
Jupyter Slide Show
Pylance
Python

it would show a tree with the following structure:

Python
|-- Jupyter
|   |-- Jupyter Keymap
|   |-- Jupyter Notebook Renderers
|   |-- Jupyter Slide Show
|   |-- Jupyter Cell Tags
|-- Pylance
|-- isort

with the ability to fold Python and Jupyter extension packs. This would make the view much cleaner and easier to use.