Treat external compositor presence as complete as internal one
For now if external compositors (e.g. picom) is enabled - this requires internal compositor to be off, causing some effects to disable unconditionally. I propose at least some compositing effects be available independently if compositor internal or not. Of course, window miniatures may be hard or impossible to have without built-in compositor, but things, depending on nothing but transparency (window switcher overlay style) should be fine with external compositing.