android client add splash page.

android/app/src/main/res/drawable/launch_background.xml

@@ -4,9 +4,9 @@
     <item android:drawable="@android:color/white" />
 
     <!-- You can insert your own image assets here -->
-    <!-- <item>
+    <item>
         <bitmap
             android:gravity="center"
-            android:src="@mipmap/launch_image" />
-    </item> -->
+            android:src="@drawable/ic_launcher_foreground" />
+    </item>
 </layer-list>

android/app/src/main/res/values/styles.xml

@@ -13,6 +13,6 @@
          
          This Theme is only used starting with V2 of Flutter's Android embedding. -->
     <style name="NormalTheme" parent="@android:style/Theme.Black.NoTitleBar">
-        <item name="android:windowBackground">@android:color/white</item>
+        <item name="android:windowBackground">@drawable/launch_background</item>
     </style>
 </resources>

android/settings_aar.gradle

@@ -0,0 +1 @@
+include ':app'