[Suggestion] Maybe have the headerbar fall back to being a menu toolbar when client decorations are disabled?

[netraptor]

So, right now if you disable client decorations you end up with something like this:

Would it be desirable to have the headerbar turn into a menu toolbar (no window dragging, no window controls) if client decorations are disabled? I'm wondering if that might be acceptable as an option in situations where OS-native window decorations are desirable (such as was mentioned in issue #523).

As seen in the picture above, window corner behavior would also need to be changed to look better within server-side decorations.