[folding] Fold all comments in a file

[DeadEye0112]

I'd like to be able to fold all the comments in a file with a shortcut, something like editor.foldAllComments.
This is probably linked to this issue : [folding] language-aware folding #3422

The idea, is to make it easier to transform a file like this :

To this :

[aeschli]

To implement what you suggest we would have to get an understanding on what a comment is.
#3422 is the first step for this.