Update null_safety Android files (#1020)

null_safety/null_unsafe_app/android/app/src/main/AndroidManifest.xml

@@ -2,9 +2,11 @@
     package="com.example.null_unsafe_app">
    <application
         android:label="null_unsafe_app"
+        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"
@@ -18,15 +20,6 @@
               android:name="io.flutter.embedding.android.NormalTheme"
               android:resource="@style/NormalTheme"
               />
-            <!-- Displays an Android View that continues showing the launch screen
-                 Drawable until Flutter paints its first frame, then this splash
-                 screen fades out. A splash screen is useful to avoid any visual
-                 gap between the end of Android's launch screen and the painting of
-                 Flutter's first frame. -->
-            <meta-data
-              android:name="io.flutter.embedding.android.SplashScreenDrawable"
-              android:resource="@drawable/launch_background"
-              />
             <intent-filter>
                 <action android:name="android.intent.action.MAIN"/>
                 <category android:name="android.intent.category.LAUNCHER"/>

null_safety/null_unsafe_app/android/app/src/main/res/drawable-v21/launch_background.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Modify this file to customize your launch splash screen -->
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="?android:colorBackground" />
+
+    <!-- You can insert your own image assets here -->
+    <!-- <item>
+        <bitmap
+            android:gravity="center"
+            android:src="@mipmap/launch_image" />
+    </item> -->
+</layer-list>

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

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <!-- Modify this file to customize your launch splash screen -->
 <layer-list xmlns:android="http://schemas.android.com/apk/res/android">
-    <item android:drawable="?android:colorBackground" />
+    <item android:drawable="@android:color/white" />
 
     <!-- You can insert your own image assets here -->
     <!-- <item>

null_safety/null_unsafe_app/android/app/src/main/res/values-night/styles.xml

@@ -10,7 +10,7 @@
          This theme determines the color of the Android Window while your
          Flutter UI initializes, as well as behind your Flutter UI while its
          running.
-         
+
          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:colorBackground</item>

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

@@ -10,7 +10,7 @@
          This theme determines the color of the Android Window while your
          Flutter UI initializes, as well as behind your Flutter UI while its
          running.
-         
+
          This Theme is only used starting with V2 of Flutter's Android embedding. -->
     <style name="NormalTheme" parent="@android:style/Theme.Light.NoTitleBar">
         <item name="android:windowBackground">?android:colorBackground</item>