Refactor ScrollBar and TextBox templates: simplify ScrollBar structure, introduce `AutoScrollViewer` in TextBox, and add `LineHeight` property for improved layout and customization.

src/PicView.Avalonia/PicViewTheme/Controls/Scrollbar.axaml

@@ -225,20 +225,19 @@
         <Setter Property="Cursor" Value="Arrow" />
 
         <Style Selector="^:horizontal">
-            <Setter Property="Height" Value="18" />
-            <Setter Property="Focusable" Value="False" />
             <Setter Property="Template">
                 <ControlTemplate>
-                    <Border Background="Transparent" UseLayoutRounding="False">
-                        <Track
-                            DeferThumbDrag="{TemplateBinding ScrollViewer.IsDeferredScrollingEnabled}"
-                            Maximum="{TemplateBinding Maximum}"
-                            Minimum="{TemplateBinding Minimum}"
-                            Orientation="{TemplateBinding Orientation}"
-                            Value="{TemplateBinding Value,
-                                                    Mode=TwoWay}"
-                            ViewportSize="{TemplateBinding ViewportSize}" />
-                    </Border>
+                    <Track
+                        DeferThumbDrag="{TemplateBinding ScrollViewer.IsDeferredScrollingEnabled}"
+                        IsDirectionReversed="True"
+                        Maximum="{TemplateBinding Maximum}"
+                        Minimum="{TemplateBinding Minimum}"
+                        Orientation="{TemplateBinding Orientation}"
+                        Value="{TemplateBinding Value,
+                                                Mode=TwoWay}"
+                        ViewportSize="{TemplateBinding ViewportSize}">
+                        <Thumb Name="thumb" />
+                    </Track>
                 </ControlTemplate>
             </Setter>
         </Style>

src/PicView.Avalonia/PicViewTheme/Controls/TextBox.axaml

@@ -1,6 +1,7 @@
 <ResourceDictionary
     x:ClassModifier="internal"
     xmlns="https://github.com/avaloniaui"
+    xmlns:customControls="clr-namespace:PicView.Avalonia.CustomControls"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
 
     <ControlTheme TargetType="TextBox" x:Key="{x:Type TextBox}">
@@ -9,6 +10,7 @@
         <Setter Property="SelectionForegroundBrush" Value="{DynamicResource MainTextColor}" />
         <Setter Property="Padding" Value="8,4,0,4" />
         <Setter Property="ScrollViewer.IsScrollChainingEnabled" Value="True" />
+        <Setter Property="LineHeight" Value="16" />
         <Setter Property="Template">
             <ControlTemplate>
                 <Border
@@ -26,13 +28,14 @@
 
                             <Grid ColumnDefinitions="Auto,*,Auto">
                                 <ContentPresenter Content="{TemplateBinding InnerLeftContent}" Grid.Column="0" />
-                                <ScrollViewer
+                                <customControls:AutoScrollViewer
                                     AllowAutoHide="{TemplateBinding (ScrollViewer.AllowAutoHide)}"
                                     BringIntoViewOnFocusChange="{TemplateBinding (ScrollViewer.BringIntoViewOnFocusChange)}"
                                     Grid.Column="1"
                                     HorizontalScrollBarVisibility="{TemplateBinding (ScrollViewer.HorizontalScrollBarVisibility)}"
                                     IsScrollChainingEnabled="{TemplateBinding (ScrollViewer.IsScrollChainingEnabled)}"
                                     Name="PART_ScrollViewer"
+                                    Theme="{StaticResource Inline}"
                                     VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}">
                                     <Panel>
                                         <TextBlock
@@ -63,12 +66,12 @@
                                             TextAlignment="{TemplateBinding TextAlignment}"
                                             TextWrapping="{TemplateBinding TextWrapping}" />
                                     </Panel>
-                                    <ScrollViewer.Styles>
+                                    <customControls:AutoScrollViewer.Styles>
                                         <Style Selector="ScrollContentPresenter#PART_ContentPresenter">
                                             <Setter Property="Cursor" Value="IBeam" />
                                         </Style>
-                                    </ScrollViewer.Styles>
-                                </ScrollViewer>
+                                    </customControls:AutoScrollViewer.Styles>
+                                </customControls:AutoScrollViewer>
                                 <ContentPresenter Content="{TemplateBinding InnerRightContent}" Grid.Column="2" />
                             </Grid>
                         </DataValidationErrors>