title: Kotlin PendingIntent with FLAG_IMMUTABLE does't work with exoplayer
body: <p>I'am using a pending intent to make a notification bar when i play a song in my music app. it used to work perfectly but i have to update my targetSdk to 31 and i run into an error telling me that i need to use some flag with my pendingIntent :</p>
  <pre><code>Targeting S+ (version 31 and above) requires that one of FLAG_IMMUTABLE or FLAG_MUTABLE be specified when creating a PendingIntent.
  Strongly consider using FLAG_IMMUTABLE, only use FLAG_MUTABLE if some functionality depends on the PendingIntent being mutable, e.g. if it needs to be used with inline replies or bubbles.
  </code></pre>
  <p>Problem is that i use this flag when i declare my pending intent :</p>
  <pre><code> val pendingIntent = PendingIntent.getActivity(
          applicationContext,
      0,
          packageManager?.getLaunchIntentForPackage(packageName),
          PendingIntent.FLAG_IMMUTABLE
      )
  </code></pre>
  <p>So i don't get why it say that i need to use the flag when i already using it ? Am I missing something ?</p>
  <p><strong>EDIT</strong></p>
  <pre><code>Strongly consider using FLAG_IMMUTABLE, only use FLAG_MUTABLE if some functionality depends on the PendingIntent being mutable, e.g. if it needs to be used with inline replies or bubbles.
          at android.app.ActivityThread.handleCreateService(ActivityThread.java:4953)
          at android.app.ActivityThread.access$1900(ActivityThread.java:310)
          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2300)
          at android.os.Handler.dispatchMessage(Handler.java:106)
          at android.os.Looper.loopOnce(Looper.java:226)
          at android.os.Looper.loop(Looper.java:313)
          at android.app.ActivityThread.main(ActivityThread.java:8663)
          at java.lang.reflect.Method.invoke(Native Method)
          at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:567)
          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1135)
       Caused by: java.lang.IllegalArgumentException: info.cairn.pro: Targeting S+ (version 31 and above) requires that one of FLAG_IMMUTABLE or FLAG_MUTABLE be specified when creating a PendingIntent.
      Strongly consider using FLAG_IMMUTABLE, only use FLAG_MUTABLE if some functionality depends on the PendingIntent being mutable, e.g. if it needs to be used with inline replies or bubbles.
          at android.app.PendingIntent.checkFlags(PendingIntent.java:382)
          at android.app.PendingIntent.getBroadcastAsUser(PendingIntent.java:673)
          at android.app.PendingIntent.getBroadcast(PendingIntent.java:660)
          at com.google.android.exoplayer2.ui.PlayerNotificationManager.createBroadcastIntent(PlayerNotificationManager.java:1601)
          at com.google.android.exoplayer2.ui.PlayerNotificationManager.createPlaybackActions(PlayerNotificationManager.java:1557)
          at com.google.android.exoplayer2.ui.PlayerNotificationManager.&lt;init&gt;(PlayerNotificationManager.java:862)
          at com.google.android.exoplayer2.ui.PlayerNotificationManager.&lt;init&gt;(PlayerNotificationManager.java:793)
          at com.google.android.exoplayer2.ui.PlayerNotificationManager.&lt;init&gt;(PlayerNotificationManager.java:757)
          at com.google.android.exoplayer2.ui.PlayerNotificationManager.createWithNotificationChannel(PlayerNotificationManager.java:729)
          at com.viapresse.presskit.exoplayer.MusicNotificationManager.&lt;init&gt;(MusicNotificationManager.kt:29)
          at com.viapresse.presskit.exoplayer.MusicService.onCreate(MusicService.kt:114)
          at android.app.ActivityThread.handleCreateService(ActivityThread.java:4940)
  </code></pre>