Call makeFirstResponder when showing window.
Call makeFirstResponder when showing window.

This is needed in order for the view to receive keyboard events immediately after showing the window.

Fixes #6202

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