Merge Window::client{Minimized,Unminimized} with Window::minimizedChanged
This merges Window::clientMinimized() and Window::clientUnminimized() signals with the Window::minimizedChanged() signal to simplify some code.
The avoid animation flag has been dropped because its main usage is to avoid playing animation during window initialization. But it's not possible to trigger minimize animation at that moment. API-wise it's better to avoid having such flags too and rely on surface role to decide whether to play a given animation.