Image size should match assets image size

[wieslawsoltes]

The .png image width and height should match Image width and height defined in xaml to avoid blurry image resizing.

• Original asset image is 32x32, xaml image is 40x40
  

  Dock/src/Dock.Avalonia/Controls/DockTarget.xaml

  Line 21 in ac60299

  <Image Name="PART_CenterSelector" Source="resm:Dock.Avalonia.Assets.DockDocumentInside.png?assembly=Dock.Avalonia" Height="40" Width="40" Grid.Row="1" Grid.Column="1" />

• Original asset image is 13x13, xaml image is 12x12
  

  Dock/src/Dock.Avalonia/Controls/DockToolChrome.xaml

  Line 13 in ac60299

  <Image Source="resm:Dock.Avalonia.Assets.PinClose_Dark.png?assembly=Dock.Avalonia" Height="12" Width="12" Stretch="None" />

• Original asset image is 13x13, xaml image is 12x12
  

  Dock/src/Dock.Avalonia/Controls/DockToolChrome.xaml

  Line 16 in ac60299

  <Image Source="resm:Dock.Avalonia.Assets.PinAutoHide_Dark.png?assembly=Dock.Avalonia" Height="12" Width="12" Stretch="None" />

• Original asset image is 13x13, xaml image is 12x12
  

  Dock/src/Dock.Avalonia/Controls/DockToolChrome.xaml

  Line 19 in ac60299

  <Image Source="resm:Dock.Avalonia.Assets.PinMenu_Dark.png?assembly=Dock.Avalonia" Height="12" Width="12" Stretch="None" />