Migrate Android example from pre-1.12 created code.

example/flutter/objectbox_demo/android/app/src/main/AndroidManifest.xml

@@ -1,28 +1,30 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="com.example.objectbox_demo">
-    <!-- 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"
         android:label="objectbox_demo"
         android:icon="@mipmap/ic_launcher">
+
+        <meta-data
+            android:name="flutterEmbedding"
+            android:value="2" />
+
         <activity
             android:name=".MainActivity"
             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">
-            <!-- This keeps the window background of the activity showing
-                 until Flutter renders its first frame. It can be removed if
-                 there is no splash screen (such as the default splash screen
-                 defined in @style/LaunchTheme). -->
+            <!-- Specify that the launch screen should continue being displayed -->
+            <!-- until Flutter renders its first frame. -->
             <meta-data
-                android:name="io.flutter.app.android.SplashScreenUntilFirstFrame"
-                android:value="true" />
+                    android:name="io.flutter.embedding.android.SplashScreenDrawable"
+                    android:resource="@drawable/launch_background" />
+
+            <!-- Theme to apply as soon as Flutter begins rendering frames -->
+            <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"/>

example/flutter/objectbox_demo/android/app/src/main/kotlin/com/example/objectbox_demo/MainActivity.kt

@@ -1,12 +1,6 @@
 package com.example.objectbox_demo
 
-import android.os.Bundle
-import io.flutter.app.FlutterActivity
-import io.flutter.plugins.GeneratedPluginRegistrant
+import io.flutter.embedding.android.FlutterActivity
 
 class MainActivity: FlutterActivity() {
-    override fun onCreate(savedInstanceState: Bundle?) {
-        super.onCreate(savedInstanceState)
-        GeneratedPluginRegistrant.registerWith(this)
-    }
 }

example/flutter/objectbox_demo/android/app/src/main/res/values/styles.xml

@@ -5,4 +5,7 @@
              Flutter draws its first frame -->
         <item name="android:windowBackground">@drawable/launch_background</item>
     </style>
+    <style name="NormalTheme" parent="@android:style/Theme.Black.NoTitleBar">
+        <item name="android:windowBackground">@drawable/launch_background</item>
+    </style>
 </resources>