Add a mutability flag to the PendingIntent

- Request from Android Platform Security team.
  go/immutable-pendingintents

Bug: 170162129
Test:
1. adb shell am start -a
android.settings.panel.action.INTERNET_CONNECTIVITY
2. make RunSettingsRoboTests ROBOTEST_FILTER=WifiSliceTest
Change-Id: If3032959649206f2fb6736244d7aa8b9a8419378