effects/invert: Make it fully responsible for inverting the screen

The X11 standalone backend has an obscure fallback to hw screen inversion if compositing is disabled. While it's great, it conflicts with existing features such as night color.

In order to make code cleaner and clean up dependencies, this change moves screen inversion shortcut to the invert effect. While it can potentially affect users that don't use compositing, I think the number of such affected people is very small.

In hindsight, preferring hw over sw transform is nice, but I think we need to analyze it first and then come up with a proper solution that integrates with color management and works great both on x11 and wayland.