Let dropdowns expand beyond Modal body in EditEvents

[gregorbg]

Really quick fix for #10522, although I'm not sure whether this breaks anything else. I did a few basic sanity checks, but I'm sure experienced Delegates have other use-cases for this panel...

Git Blame shows that we introduced the scrolling property only in #8765, which was targeted towards a specific issue with scrolling in a long list of cumulative rounds. I have changed the code so that each nested modal can decide by itself whether it wants to be scrolling or not, although the new default value is false (as opposed to before. when every modal was scrolling by default, which caused the issue with dropdowns)

[kr-matthews]

This is also an issue with editing advancement conditions, so the same changes should be applied there. But even if I add contentScrolling there, it still looks like this:

[gregorbg]

The point is that enabling contentScrolling is what causes the dropdown glitch. In a sense, enabling the scrollbar is precisely what "swallows" the dropdown.

The solution is to make sure that it is disabled for popups where you don't want this problem to happen. That's why the default value is set to false, and you should only enable it at all on dropdowns that have a lot of content (like the radio buttons in the cumulative cutoff window).