Fixed DropDownItem alignment.
Fixed DropDownItem alignment.

This makes the DropDown with control items in ControlCatalog display
correctly.

MrDaedra/Avalonia,punker76/Perspex,grokys/Perspex,jkoritzinsky/Avalonia,jazzay/Perspex,AvaloniaUI/Avalonia,OronDF343/Avalonia,AvaloniaUI/Avalonia,jkoritzinsky/Avalonia,jkoritzinsky/Perspex,SuperJMN/Avalonia,jkoritzinsky/Avalonia,SuperJMN/Avalonia,susloparovdenis/Avalonia,MrDaedra/Avalonia,SuperJMN/Avalonia,jkoritzinsky/Avalonia,SuperJMN/Avalonia,wieslawsoltes/Perspex,susloparovdenis/Perspex,jkoritzinsky/Avalonia,wieslawsoltes/Perspex,wieslawsoltes/Perspex,susloparovdenis/Perspex,jkoritzinsky/Avalonia,AvaloniaUI/Avalonia,AvaloniaUI/Avalonia,AvaloniaUI/Avalonia,SuperJMN/Avalonia,AvaloniaUI/Avalonia,wieslawsoltes/Perspex,SuperJMN/Avalonia,akrisiun/Perspex,susloparovdenis/Avalonia,wieslawsoltes/Perspex,SuperJMN/Avalonia,jkoritzinsky/Avalonia,Perspex/Perspex,grokys/Perspex,wieslawsoltes/Perspex,wieslawsoltes/Perspex,Perspex/Perspex,OronDF343/Avalonia,AvaloniaUI/Avalonia