Explicitly declare `android:exported` in examples' manifest (#88502)

examples/flutter_view/android/app/src/main/AndroidManifest.xml

@@ -12,6 +12,7 @@ found in the LICENSE file. -->
 
     <application android:label="flutter_view" android:icon="@mipmap/ic_launcher">
         <activity android:name=".MainActivity"
+                  android:exported="true"
                   android:launchMode="singleTop"
                   android:theme="@style/Theme.AppCompat"
                   android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"

examples/hello_world/android/app/src/main/AndroidManifest.xml

@@ -13,6 +13,7 @@ found in the LICENSE file. -->
 
     <application android:label="hello_world" android:icon="@mipmap/ic_launcher">
         <activity android:name="io.flutter.embedding.android.FlutterActivity"
+                  android:exported="true"
                   android:theme="@android:style/Theme.Black.NoTitleBar"
                   android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
                   android:hardwareAccelerated="true"

examples/image_list/android/app/src/main/AndroidManifest.xml

@@ -12,6 +12,7 @@ found in the LICENSE file. -->
         android:icon="@mipmap/ic_launcher">
         <activity
             android:name="io.flutter.embedding.android.FlutterActivity"
+            android:exported="true"
             android:theme="@style/LaunchTheme"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
             android:hardwareAccelerated="true"

examples/layers/android/app/src/main/AndroidManifest.xml

@@ -13,6 +13,7 @@ found in the LICENSE file. -->
 
     <application android:label="Flutter Layers" android:icon="@mipmap/ic_launcher">
         <activity android:name="io.flutter.embedding.android.FlutterActivity"
+                  android:exported="true"
                   android:theme="@android:style/Theme.Black.NoTitleBar"
                   android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
                   android:hardwareAccelerated="true"

examples/platform_channel/android/app/src/main/AndroidManifest.xml

@@ -14,6 +14,7 @@ found in the LICENSE file. -->
 
     <application android:label="@string/app_name">
         <activity android:name=".MainActivity"
+                  android:exported="true"
                   android:launchMode="singleTop"
                   android:theme="@android:style/Theme.Black.NoTitleBar"
                   android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"

examples/platform_view/android/app/src/main/AndroidManifest.xml

@@ -16,6 +16,7 @@ found in the LICENSE file. -->
         android:label="platform_view">
         <activity
             android:name="io.flutter.examples.platform_view.MainActivity"
+            android:exported="true"
             android:theme="@android:style/Theme.Black.NoTitleBar"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
             android:hardwareAccelerated="true"