Added OpacityMask example to ControlCatalog.
Added OpacityMask example to ControlCatalog.

AvaloniaUI/Avalonia,MrDaedra/Avalonia,AvaloniaUI/Avalonia,wieslawsoltes/Perspex,wieslawsoltes/Perspex,SuperJMN/Avalonia,susloparovdenis/Avalonia,jazzay/Perspex,jkoritzinsky/Avalonia,AvaloniaUI/Avalonia,susloparovdenis/Perspex,grokys/Perspex,SuperJMN/Avalonia,jkoritzinsky/Avalonia,AvaloniaUI/Avalonia,susloparovdenis/Avalonia,AvaloniaUI/Avalonia,wieslawsoltes/Perspex,Perspex/Perspex,jkoritzinsky/Avalonia,jkoritzinsky/Avalonia,AvaloniaUI/Avalonia,jkoritzinsky/Avalonia,SuperJMN/Avalonia,jkoritzinsky/Perspex,SuperJMN/Avalonia,wieslawsoltes/Perspex,MrDaedra/Avalonia,Perspex/Perspex,wieslawsoltes/Perspex,AvaloniaUI/Avalonia,jkoritzinsky/Avalonia,jkoritzinsky/Avalonia,OronDF343/Avalonia,akrisiun/Perspex,SuperJMN/Avalonia,SuperJMN/Avalonia,wieslawsoltes/Perspex,susloparovdenis/Perspex,SuperJMN/Avalonia,wieslawsoltes/Perspex,grokys/Perspex,OronDF343/Avalonia