Invalid XAML produced when gradient defined outside defs
I think it's AWESOME that InkScape saves as XAML, and I often see it recommended for such work.
When saving this SVG as XAML, the result needs some manual modifications to make it valid in a WPF Window.
#### Steps to reproduce:
Save the SVG as a XAML file.
![favicon-src2.svg]
Copy the ViewBox from the XAML to a WPF Window.
#### What happened?
WPF designer complained that the XAML is invalid because:
LinearGradientBrush is not inside resource dictionary, eg <Canvas.Resources>
Duplicate x:Key used for brushes (this appeared after my manual fix to the XAML).
Eg.
```
<Canvas Name="layer1">
<Canvas.RenderTransform>
<TranslateTransform X="0" Y="-852.36225"/>
</Canvas.RenderTransform>
<Canvas Name="g5191" Opacity="0.71399997">
<Canvas.RenderTransform>
<MatrixTransform Matrix="1.2992849 0 0 1.1048786 23.192244 857.41524"/>
</Canvas.RenderTransform>
<LinearGradientBrush xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" x:Key="linearGradient5047" MappingMode="Absolute" StartPoint="50,0" EndPoint="50,164">
<LinearGradientBrush.GradientStops>
```
#### What should have happened?
Presumably there is an element missing in the XAML that should have wrapped the LinearGradientBrush.
#### Inkscape Version and Operating System:
- Inkscape Version: 0.91 and 0.92
- Operating System: Windows
- Operating System version: 10
[favicon-src.xaml](/uploads/77ff47cf8dd478afa30718367b61b42b/favicon-src.xaml)
issue