Disabled TextBox BorderThickness bugfix, fixes #893 (#912)

Thank you. Great work. Sorry it took so long to get it merged.

Author: JeffBarnard

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.ComboBox.xaml

@@ -488,7 +488,7 @@
                 </Grid>
                 <Line x:Name="DashedLine" Grid.ColumnSpan="2" Grid.Column="0" VerticalAlignment="Bottom"
                       Visibility="{Binding Path=IsEnabled, RelativeSource={RelativeSource Self}, Converter={StaticResource InverseBoolToVisConverter}}"
-                      StrokeThickness="1.25" StrokeDashArray="1,2.5" StrokeDashCap="Round"
+                      StrokeThickness="{Binding BorderThickness.Bottom, ElementName=toggleButton, Converter={StaticResource DivisionMathConverter}, ConverterParameter=0.75}" StrokeDashArray="1,2.5" StrokeDashCap="Round"
                       X1="0" X2="{Binding ActualWidth, ElementName=toggleButton}" Y1="0" Y2="0" 
                       Stroke="{TemplateBinding BorderBrush}" Opacity="0.56" />
                 <wpf:Underline x:Name="Underline"

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.PasswordBox.xaml

@@ -8,6 +8,7 @@
     </ResourceDictionary.MergedDictionaries>
 
     <converters:BooleanToVisibilityConverter x:Key="InverseBoolToVisConverter" TrueValue="Collapsed" FalseValue="Visible"/>
+    <converters:MathConverter Operation="Divide" x:Key="DivisionMathConverter" />
     <converters:TextFieldClearButtonVisibilityConverter x:Key="ClearTextConverter" />
     <converters:NotConverter x:Key="NotConverter" />
 
@@ -144,7 +145,8 @@
                                         VerticalAlignment="Bottom"
                                         SnapsToDevicePixels="True" />
                                 <Line x:Name="DashedLine" VerticalAlignment="Bottom" Visibility="Hidden"
-                                      StrokeThickness="1.25" StrokeDashArray="1,2.5" StrokeDashCap="Round"
+                                      StrokeThickness="{Binding BorderThickness.Bottom, ElementName=border, Converter={StaticResource DivisionMathConverter}, ConverterParameter=0.75}" 
+                                      StrokeDashArray="1,2.5" StrokeDashCap="Round"
                                       X1="0" X2="{Binding ActualWidth, ElementName=border}" Y1="0" Y2="0"
                                       Stroke="{TemplateBinding BorderBrush}" Opacity="0.56" />
                                 <wpf:Underline x:Name="Underline" Visibility="{Binding Path=(wpf:TextFieldAssist.DecorationVisibility), RelativeSource={RelativeSource TemplatedParent}}"

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.TextBox.xaml

@@ -8,6 +8,7 @@
     </ResourceDictionary.MergedDictionaries>
 
     <converters:TextFieldHintVisibilityConverter x:Key="TextFieldHintVisibilityConverter" />
+    <converters:MathConverter Operation="Divide" x:Key="DivisionMathConverter" />
     <converters:BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter" />
     <converters:TextFieldClearButtonVisibilityConverter x:Key="ClearTextConverter" />
     <converters:NotConverter x:Key="NotConverter" />
@@ -153,7 +154,8 @@
                                         SnapsToDevicePixels="True" />
                                 <Line x:Name="DashedLine" VerticalAlignment="Bottom" Visibility="Collapsed"
                                       X1="0" X2="{Binding ActualWidth, ElementName=border}" Y1="0" Y2="0" 
-                                      StrokeThickness="1.25" StrokeDashArray="1,2.5" StrokeDashCap="Round"
+                                      StrokeThickness="{Binding BorderThickness.Bottom, ElementName=border, Converter={StaticResource DivisionMathConverter}, ConverterParameter=0.75}" 
+                                      StrokeDashArray="1,2.5" StrokeDashCap="Round"
                                       Stroke="{TemplateBinding BorderBrush}" Opacity="0.56" />
                                 <wpf:Underline x:Name="Underline" Visibility="{Binding Path=(wpf:TextFieldAssist.DecorationVisibility), RelativeSource={RelativeSource TemplatedParent}}"
                                                CornerRadius="{Binding Path=(wpf:TextFieldAssist.UnderlineCornerRadius), RelativeSource={RelativeSource TemplatedParent}}"