fix implementation of ScalingChanged property.
fix implementation of ScalingChanged property.

there were 2x implementations, 1x implicit, 1x explicit... :face-palm:

grokys/Perspex,Perspex/Perspex,jkoritzinsky/Avalonia,SuperJMN/Avalonia,Perspex/Perspex,jkoritzinsky/Avalonia,SuperJMN/Avalonia,AvaloniaUI/Avalonia,grokys/Perspex,AvaloniaUI/Avalonia,SuperJMN/Avalonia,AvaloniaUI/Avalonia,SuperJMN/Avalonia,SuperJMN/Avalonia,wieslawsoltes/Perspex,jkoritzinsky/Avalonia,wieslawsoltes/Perspex,AvaloniaUI/Avalonia,jkoritzinsky/Avalonia,AvaloniaUI/Avalonia,wieslawsoltes/Perspex,SuperJMN/Avalonia,jkoritzinsky/Perspex,wieslawsoltes/Perspex,jkoritzinsky/Avalonia,jkoritzinsky/Avalonia,SuperJMN/Avalonia,wieslawsoltes/Perspex,wieslawsoltes/Perspex,AvaloniaUI/Avalonia,wieslawsoltes/Perspex,jkoritzinsky/Avalonia,AvaloniaUI/Avalonia