Theming fixes (#1236)

* Fix TextControl placeholders not using the proper color

* Fix InfoBar padding so it's centered for single-line messages

Author: Difegue

src/Wpf.Ui/Controls/InfoBar/InfoBar.xaml

@@ -40,7 +40,7 @@
                     <Grid x:Name="InfoBarRoot">
                         <Border
                             x:Name="ContentBorder"
-                            Padding="16,14,16,10"
+                            Padding="16,12"
                             HorizontalAlignment="{TemplateBinding HorizontalAlignment}"
                             VerticalAlignment="{TemplateBinding VerticalAlignment}"
                             Background="{TemplateBinding Background}"

src/Wpf.Ui/Resources/Theme/Dark.xaml

@@ -594,7 +594,7 @@
     <SolidColorBrush x:Key="TextControlForegroundDisabled" Color="{StaticResource TextFillColorDisabled}" />
     <SolidColorBrush x:Key="TextControlFocusedBorderBrush" Color="{DynamicResource SystemAccentColorPrimary}" />
     <SolidColorBrush x:Key="TextControlBorderBrushDisabled" Color="{StaticResource ControlStrokeColorDefault}" />
-    <SolidColorBrush x:Key="TextControlPlaceholderForeground" Color="{StaticResource TextFillColorSecondary}" />
+    <SolidColorBrush x:Key="TextControlPlaceholderForeground" Color="{StaticResource TextPlaceholderColor}" />
     <SolidColorBrush x:Key="TextControlButtonForeground" Color="{StaticResource TextFillColorSecondary}" />
 
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src/Wpf.Ui/Resources/Theme/Light.xaml

@@ -595,7 +595,7 @@
     <SolidColorBrush x:Key="TextControlForegroundDisabled" Color="{StaticResource TextFillColorDisabled}" />
     <SolidColorBrush x:Key="TextControlFocusedBorderBrush" Color="{DynamicResource SystemAccentColorPrimary}" />
     <SolidColorBrush x:Key="TextControlBorderBrushDisabled" Color="{StaticResource ControlStrokeColorDefault}" />
-    <SolidColorBrush x:Key="TextControlPlaceholderForeground" Color="{StaticResource TextFillColorSecondary}" />
+    <SolidColorBrush x:Key="TextControlPlaceholderForeground" Color="{StaticResource TextPlaceholderColor}" />
     <SolidColorBrush x:Key="TextControlButtonForeground" Color="{StaticResource TextFillColorSecondary}" />
 
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