Fold/Unfold action does not support multiple regions

[weinand]

On testing #2994

In this snippet range select both 'foo' and 'bar' methods and then perform 'Fold' operation.

class xyz {
    foo() {
        hello
    }
    bar() {
        world
    }
}

Observe: only 'foo' is collapsed.
I would expect that all regions overlapping with the text selection are collapsed.

[aeschli]

duplicate of #3403