feat: rename theme key.

demo/Semi.Avalonia.Demo/Pages/HeaderedContentControlDemo.axaml

@@ -5,7 +5,7 @@
              mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
              x:Class="Semi.Avalonia.Demo.Pages.HeaderedContentControlDemo">
     <ScrollViewer>
-        <HeaderedContentControl Header="Semi Design">
+        <HeaderedContentControl Theme="{DynamicResource GroupBox}" Header="Semi Design">
             <TextBlock TextWrapping="Wrap">Semi Design 是由互娱社区前端团队与 UED 团队共同设计开发并维护的设计系统。设计系统包含设计语言以及一整套可复用的前端组件，帮助设计师与开发者更容易地打造高质量的、用户体验一致的、符合设计规范的 Web 应用。</TextBlock>
         </HeaderedContentControl>
     </ScrollViewer>

src/Semi.Avalonia/Controls/HeaderedContentControl.axaml

@@ -2,7 +2,7 @@
     xmlns="https://github.com/avaloniaui"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     x:CompileBindings="True">
-    <ControlTheme x:Key="{x:Type HeaderedContentControl}" TargetType="HeaderedContentControl">
+    <ControlTheme x:Key="GroupBox" TargetType="HeaderedContentControl">
         <Setter Property="Background" Value="{DynamicResource HeaderedContentControlDefaultBackground}" />
         <Setter Property="BorderThickness" Value="1" />
         <Setter Property="BorderBrush" Value="{DynamicResource HeaderedContentControlDefaultBorderBrush}" />