[Bug][Android] Missing exported properties in activity element

[duarteroso]

Issue description:
When setting the target SDK version to the minimum mandatory version, an error is thrown due to a missing property in the activity element of the AndroidManifest.

<activity android:name="com.flaxengine.GameActivity"
            android:exported="true" // <-- Missing and mandatory since August 2023 (API level 33 requirement)
            android:label="@string/app_name"
            android:configChanges="orientation|keyboardHidden|screenSize"
            android:screenOrientation="fullSensor">
            <meta-data android:name="android.app.lib_name" android:value="FlaxGame" />
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
</activity>

Steps to reproduce:

1. Export to Android
2. Set target sdk version to 33 (mandatory to publish on Google Play Store)
3. An error will be throw about missing exported property in the activity element of the AndroidManifest file

Minimal reproduction project: N/A
Flax version: 1.8.0