`movable_by_window_background` breaks slider and text selections on macos

[dominikwilkowski]

I just bumped floem to latest after the text selection PR got merged. I found that since I use movable_by_window_background it breaks and gets caught in an infinite loop of There is an available text layout output in the console.

Sliders also break with that window option.

Perhaps we should find a way to define areas around certain interactive elements that don't act like "background" for the movable_by_window_background option?