[Bugfix][Android] Use JobServiceIntent to fetch the FCM token in the …

…background (#678)

### Highlights
- Changes the mechanism by which the library fetches the FCM token in the background.

### Context
In newer Android versions (8+), background applications cannot start `IntentService`'s. Using the notifications library in these newer Android versions will result in a lot of exceptions of the type `java.lang.IllegalStateException`. Sample stack trace:

```
java.lang.IllegalStateException: 
  at android.app.ContextImpl.startServiceCommon (ContextImpl.java:1522)
  at android.app.ContextImpl.startService (ContextImpl.java:1478)
  at android.content.ContextWrapper.startService (ContextWrapper.java:650)
  at com.wix.reactnativenotifications.RNNotificationsModule.startFcmIntentService (RNNotificationsModule.java:135)
  at com.wix.reactnativenotifications.RNNotificationsModule.initialize (RNNotificationsModule.java:50)
  at com.facebook.react.bridge.ModuleHolder.doInitialize (ModuleHolder.java:222)
  at com.facebook.react.bridge.ModuleHolder.markInitializable (ModuleHolder.java:97)
  at com.facebook.react.bridge.NativeModuleRegistry.notifyJSInstanceInitialized (NativeModuleRegistry.java:102)
  at com.facebook.react.bridge.CatalystInstanceImpl$2.run (CatalystInstanceImpl.java:441)
  at android.os.Handler.handleCallback (Handler.java:790)
  at android.os.Handler.dispatchMessage (Handler.java:99)
  at com.facebook.react.bridge.queue.MessageQueueThreadHandler.dispatchMessage (MessageQueueThreadHandler.java:26)
  at android.os.Looper.loop (Looper.java:164)
  at com.facebook.react.bridge.queue.MessageQueueThreadImpl$4.run (MessageQueueThreadImpl.java:225)
  at java.lang.Thread.run (Thread.java:764)
```

Now, in order to start intents in the background, the `JobIntentService` class must be extended.

This PR consists in basically the same changes proposed by @migbot in #491 (this PR was closed for inactivity a few months ago).

Should close #671;

lib/android/app/src/main/AndroidManifest.xml

@@ -20,7 +20,8 @@
 
         <service
             android:name=".fcm.FcmInstanceIdRefreshHandlerService"
-            android:exported="false" />
+            android:exported="false"
+            android:permission="android.permission.BIND_JOB_SERVICE" />
     </application>
 
 </manifest>

lib/android/app/src/main/java/com/wix/reactnativenotifications/RNNotificationsModule.java

@@ -144,6 +144,6 @@ protected void startFcmIntentService(String extraFlag) {
         final Context appContext = getReactApplicationContext().getApplicationContext();
         final Intent tokenFetchIntent = new Intent(appContext, FcmInstanceIdRefreshHandlerService.class);
         tokenFetchIntent.putExtra(extraFlag, true);
-        appContext.startService(tokenFetchIntent);
+        FcmInstanceIdRefreshHandlerService.enqueueWork(appContext, tokenFetchIntent);
     }
 }

lib/android/app/src/main/java/com/wix/reactnativenotifications/fcm/FcmInstanceIdRefreshHandlerService.java

@@ -1,19 +1,22 @@
 package com.wix.reactnativenotifications.fcm;
 
-import android.app.IntentService;
+import androidx.annotation.NonNull;
+import androidx.core.app.JobIntentService;
+import android.content.Context;
 import android.content.Intent;
 
-public class FcmInstanceIdRefreshHandlerService extends IntentService {
+public class FcmInstanceIdRefreshHandlerService extends JobIntentService {
 
     public static String EXTRA_IS_APP_INIT = "isAppInit";
     public static String EXTRA_MANUAL_REFRESH = "doManualRefresh";
+    public static final int JOB_ID = 2400;
 
-    public FcmInstanceIdRefreshHandlerService() {
-        super(FcmInstanceIdRefreshHandlerService.class.getSimpleName());
+    public static void enqueueWork(Context context, Intent work) {
+        enqueueWork(context, FcmInstanceIdRefreshHandlerService.class, JOB_ID, work);
     }
 
     @Override
-    protected void onHandleIntent(Intent intent) {
+    protected void onHandleWork(@NonNull Intent intent) {
         IFcmToken fcmToken = FcmToken.get(this);
         if (fcmToken == null) {
             return;