Offline plugin: java.lang.IllegalStateException - Missing theme on OfflineActivity

还没有人认领这个 Issue。

I received the following crash log from Firebase Crashlytics:
```
Fatal Exception: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.cohenadair.anglerslog/com.mapbox.mapboxsdk.plugins.offline.ui.OfflineActivity}: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
at android.app.ActivityThread.-wrap11()
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Method.java)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
```

Environment:
* Android 8.1.0, Nexus 5X
* I'm using the unofficial Flutter plugin: https://github.com/flutter-mapbox-gl
* The Flutter plugin uses:
```
dependencies {
implementation "com.mapbox.mapboxsdk:mapbox-android-sdk:9.6.2"
implementation "com.mapbox.mapboxsdk:mapbox-android-plugin-annotation-v9:0.9.0"
implementation "com.mapbox.mapboxsdk:mapbox-android-plugin-localization-v9:0.12.0"
implementation 'com.mapbox.mapboxsdk:mapbox-android-plugin-offline-v9:0.7.0'
}
```

Notes:
* I'm not quite sure how to reproduce it. I loaded a map on an Android 8 (and 12) emulator while not having an internet connection, and although the map appeared black, the app did not crash.

Start at the OfflineActivity entry point and inspect how its Android theme is configured when launched by the offline plugin. Try to reproduce the reported launch failure with the supplied Mapbox SDK and offline plugin versions; done means OfflineActivity starts without the reported AppCompat theme exception.

由索引模型根据 Issue 内容生成。