LibGUI: Splitters can grow their windows (new layout system issue)

[thankyouverycool]

https://user-images.githubusercontent.com/66646555/178268553-ccae1ae5-c25e-47a3-848d-ece77d47e4ad.mp4

Dragging a splitter beyond the minimum size of an unfixed resizee resizes the fixed resizee and by extension the window an amount equal to the distance traveled across the unfixed resizee.