[folding] Preview folded content on hover

[ColCh]

Found no existing issues

It would be cool to preview folded content without actual unfolding it, using peek

For example, how it's done in WebStorm:

small gif

video: https://streamable.com/i8z3u

I think it should be in core. Or a plugin which distributes with vscode. What do you think?

refs for code:

css: https://github.com/Microsoft/vscode/blob/cb66c137e0279693a8fcea3ed481d1d2db7512c7/src/vs/editor/contrib/folding/folding.css

ts: https://github.com/Microsoft/vscode/blob/4e4e6f9b44dd9e6a53d1f08565c52b8ea9f61a5e/src/vs/editor/contrib/folding/foldingDecorations.ts

[PEZ]

This would be perfect for presenting folded data structures. Like I ask for here: #81313