Add bubble hint to guide users to review the selected changes after clicking Default Mode button (#519)

Schemas/BubbleHint.xaml

@@ -0,0 +1,41 @@
+<Grid xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+      Name="BubblePanel"
+      SnapsToDevicePixels="True">
+    <Grid.RowDefinitions>
+        <RowDefinition Height="Auto"/>
+        <RowDefinition Height="Auto"/>
+    </Grid.RowDefinitions>
+
+    <Border Name="BubbleBorder"
+            Grid.Row="0"
+            Background="{DynamicResource CardBgColor}"
+            BorderBrush="{DynamicResource ButtonBorderColor}"
+            BorderThickness="1"
+            CornerRadius="8"
+            Padding="10,7,10,7">
+        <TextBlock Name="BubbleText"
+                   Text="View the selected changes here"
+                   TextWrapping="Wrap"
+                   MaxWidth="260"
+                   Foreground="{DynamicResource FgColor}"/>
+    </Border>
+
+    <Grid Grid.Row="1"
+          HorizontalAlignment="Center"
+          Margin="0,-1,0,0"
+          Width="12"
+          Height="8">
+        <Polygon Name="BubblePointer"
+                 Points="0,0 12,0 6,7"
+                 Fill="{DynamicResource CardBgColor}"
+                 Stroke="{DynamicResource ButtonBorderColor}"
+                 StrokeThickness="1"
+                 Stretch="Fill"/>
+
+        <Rectangle VerticalAlignment="Top"
+                   Height="2"
+                   Margin="1,-1,1,0"
+                   Fill="{DynamicResource CardBgColor}"/>
+    </Grid>
+</Grid>