Update platform_design Android files (#1023)

platform_design/android/app/src/main/AndroidManifest.xml

@@ -1,21 +1,25 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="dev.flutter.platform_design">
-    <!-- io.flutter.app.FlutterApplication is an android.app.Application that
-         calls FlutterMain.startInitialization(this); in its onCreate method.
-         In most cases you can leave this as-is, but you if you want to provide
-         additional functionality it is fine to subclass or reimplement
-         FlutterApplication and put your custom class here. -->
-    <application
-        android:name="io.flutter.app.FlutterApplication"
+   <application
         android:label="platform_design"
+        android:name="${applicationName}"
         android:icon="@mipmap/ic_launcher">
         <activity
             android:name=".MainActivity"
+            android:exported="true"
             android:launchMode="singleTop"
             android:theme="@style/LaunchTheme"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
             android:hardwareAccelerated="true"
             android:windowSoftInputMode="adjustResize">
+            <!-- Specifies an Android theme to apply to this Activity as soon as
+                 the Android process has started. This theme is visible to the user
+                 while the Flutter UI initializes. After that, this theme continues
+                 to determine the Window background behind the Flutter UI. -->
+            <meta-data
+              android:name="io.flutter.embedding.android.NormalTheme"
+              android:resource="@style/NormalTheme"
+              />
             <intent-filter>
                 <action android:name="android.intent.action.MAIN"/>
                 <category android:name="android.intent.category.LAUNCHER"/>