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.