refactor LeftMainContent control of demo

src/Shared/HandyControlDemo_Shared/UserControl/Controls/DrawerDemoCtl.xaml

@@ -0,0 +1,8 @@
+<UserControl x:Class="HandyControlDemo.UserControl.DrawerDemoCtl"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             Background="{DynamicResource RegionBrush}">
+    <Grid>
+            
+    </Grid>
+</UserControl>

src/Shared/HandyControlDemo_Shared/UserControl/Controls/DrawerDemoCtl.xaml.cs

@@ -0,0 +1,10 @@
+namespace HandyControlDemo.UserControl
+{
+    public partial class DrawerDemoCtl
+    {
+        public DrawerDemoCtl()
+        {
+            InitializeComponent();
+        }
+    }
+}