优化更新代码，添加界面功能并整合

WPFluent/Controls/NavigationView/NavigationViewItemSeparator.xaml

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+<!--
+    This Source Code Form is subject to the terms of the MIT License.
+    If a copy of the MIT was not distributed with this file, You can obtain one at https://opensource.org/licenses/MIT.
+    Copyright (C) Leszek Pomianowski and WPF UI Contributors.
+    All Rights Reserved.
+-->
+
+<ResourceDictionary
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:controls="clr-namespace:WPFluent.Controls">
+
+    <Style TargetType="{x:Type controls:NavigationViewItemSeparator}">
+        <Setter Property="BorderBrush" Value="{DynamicResource NavigationViewItemSeparatorForeground}" />
+        <Setter Property="Background" Value="Transparent" />
+        <Setter Property="Margin" Value="0,4" />
+        <Setter Property="BorderThickness" Value="1,1,0,0" />
+        <Setter Property="SnapsToDevicePixels" Value="True" />
+        <Setter Property="OverridesDefaultStyle" Value="True" />
+        <Setter Property="Template">
+            <Setter.Value>
+                <ControlTemplate TargetType="{x:Type controls:NavigationViewItemSeparator}">
+                    <Border
+                        Width="{TemplateBinding Width}"
+                        Margin="{TemplateBinding Margin}"
+                        Background="{TemplateBinding Background}"
+                        BorderBrush="{TemplateBinding BorderBrush}"
+                        BorderThickness="{TemplateBinding BorderThickness}" />
+                </ControlTemplate>
+            </Setter.Value>
+        </Setter>
+    </Style>
+
+</ResourceDictionary>