bump targetSdkVersion to 30

Following the example of #1440 (closed), I'm opening a new issue to track all the things that need to happen to do the next targetSdkVersion bump. This also should track the scheduling. As of now, it is at 28 with nothing requiring us to go higher in the imminent future.

android-29

• forced to use androidx libs
• requires new android.permission.ACCESS_BACKGROUND_LOCATION
• requestLegacyExternalStorage
• (#2651 (closed)) replace usage of WifiManager.setWifiEnabled() https://developer.android.com/about/versions/10/privacy/changes#enable-disable-wifi

android-30

• remove all uses of AsyncTask, "deprecated in API level 30" https://developer.android.com/reference/android/os/AsyncTask
• check whether "Scoped storage enforcement" affects SDCard/USB repos https://developer.android.com/about/versions/11/privacy/storage#scoped-storage (should be fixed by !1277 (merged))
• requires QUERY_ALL_PACKAGES, see:
  • https://developer.android.com/training/basics/intents/package-visibility#all-apps
  • https://medium.com/androiddevelopers/package-visibility-in-android-11-cc857f221cd9
  • https://developer.android.com/about/versions/11/privacy/package-visibility
• Bluetooth permissions https://stackoverflow.com/questions/70746934/android-12-bluetooth-permissions / https://developer.android.com/guide/topics/connectivity/bluetooth/permissions