feat: Add DatePicker, move some common styles to shared.

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

@@ -0,0 +1,15 @@
+<UserControl
+    x:Class="Semi.Avalonia.Demo.Pages.DatePickerDemo"
+    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">
+    <StackPanel Margin="20" Spacing="20">
+        <DatePicker />
+        <DatePicker DayFormat="d (ddd)" YearVisible="False" />
+        <DatePicker IsEnabled="False" />
+    </StackPanel>
+</UserControl>

demo/Semi.Avalonia.Demo/Pages/DatePickerDemo.axaml.cs

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

demo/Semi.Avalonia.Demo/Views/MainView.axaml

@@ -36,6 +36,9 @@
         <TabItem Header="ComboBox">
             <pages:ComboBoxDemo />
         </TabItem>
+        <TabItem Header="DatePicker">
+            <pages:DatePickerDemo />
+        </TabItem>
         <TabItem Header="Expander">
             <pages:ExpanderDemo />
         </TabItem>