feat: add TextBox theme.

src/Semi.Avalonia.Demo/MainWindow.axaml

@@ -29,6 +29,9 @@
         <TabItem Header="TabControl">
             <pages:TabControlDemo />
         </TabItem>
+        <TabItem Header="TextBox">
+            <pages:TextBoxDemo />
+        </TabItem>
         <TabItem Header="RepeatButton">
             <pages:RepeatButtonDemo />
         </TabItem>

src/Semi.Avalonia.Demo/Pages/TextBoxDemo.axaml

@@ -0,0 +1,22 @@
+<UserControl
+    x:Class="Semi.Avalonia.Demo.Pages.TextBoxDemo" xmlns="https://github.com/avaloniaui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" d:DesignHeight="450"
+    d:DesignWidth="800" mc:Ignorable="d">
+    <ScrollViewer>
+        <StackPanel HorizontalAlignment="Left" Spacing="20">
+            <TextBox Width="300" />
+            <TextBox Width="300" Watermark="Please use this" />
+            <TextBox Width="300" InnerLeftContent="http://" />
+            <TextBox Width="300" InnerRightContent=".com" />
+            <TextBox
+                Width="500" InnerLeftContent="http://"
+                InnerRightContent=".com" />
+            <TextBox Width="300" Classes="clearButton" />
+            <TextBox Width="300" PasswordChar="*" />
+            <TextBox
+                Width="300" Classes="revealPasswordButton"
+                PasswordChar="*" />
+        </StackPanel>
+    </ScrollViewer>
+</UserControl>

src/Semi.Avalonia.Demo/Pages/TextBoxDemo.axaml.cs

@@ -0,0 +1,18 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace Semi.Avalonia.Demo.Pages;
+
+public partial class TextBoxDemo : UserControl
+{
+    public TextBoxDemo()
+    {
+        InitializeComponent();
+    }
+
+    private void InitializeComponent()
+    {
+        AvaloniaXamlLoader.Load(this);
+    }
+}