audioplayer needs to set FLAG_IMMUTABLE on pending intent

[xster]

Starting on Android S, the creation of PendingIntents like https://github.com/google/flutter.plugins/blob/master/packages/audiofileplayer/android/src/main/java/com/google/flutter/plugins/audiofileplayer/AudiofileplayerPlugin.java#L680 will also need to specify whether the intent is mutable or not according to https://developer.android.com/about/versions/12/behavior-changes-12#pending-intent-mutability.

cc @monkeyswarm

[rguntha]

I am also facing the same issue. Please help

[rguntha]

I have forked the branch and fixed the issue. Also sent a pull request.

https://github.com/rguntha/flutter.plugins.git