Support Other XML Namespaces

[srsgores]

Using alternative xmlns namespaces, vsXen will not be active. For example, in my Avalonia project, tab completion does not work:

<Window xmlns="https://github.com/avaloniaui" MinWidth="500" MinHeight="300">
    <TextBlock Classes="h1">Hello world!</TextBlock>
</Window>

But will work on a custom control:

<UserControl x:Class="AvaloniaApplication2.UserControl1"
            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
            xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
            xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
            xmlns:local="clr-namespace:AvaloniaApplication2"
            mc:Ignorable="d"
            d:DesignHeight="300" d:DesignWidth="300">
</UserControl>