[feat] allow to emit events on android MainActivity

[zhangsan946]

Describe the problem

I wanna to make my app reponsible to the config change.

Describe the solution you'd like

As per https://tauri.app/develop/plugins/develop-mobile/#plugin-events, the trigger function only works in plugins. But the config change handler should be defined in MainActivity.

<activity android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|smallestScreenSize|screenLayout|uiMode">
</activity>

class MainActivity : TauriActivity() {
    override fun onConfigurationChanged(newConfig: Configuration) {
        ...
    }
}

Can we support trigger function in MainActivity as well?

Alternatives considered

No response

Additional context

No response