Decouple `IWindow.Focused` from `INativeWindow.Focused` and make it abstract
Decouple `IWindow.Focused` from `INativeWindow.Focused` and make it abstract

ppy/osu-framework,smoogipooo/osu-framework,ppy/osu-framework,smoogipooo/osu-framework,peppy/osu-framework,ppy/osu-framework,peppy/osu-framework,peppy/osu-framework