[testapp] fixup onSaveInstanceState usage

[tobrun]

This PR fixes up the usage of Activity#OnSaveInstanceState:

override fun onSaveInstanceState(outState: Bundle?, outPersistentState: PersistableBundle?) {
    super.onSaveInstanceState(outState, outPersistentState)
    outState?.let {
      mapView.onSaveInstanceState(it)
    }
  }

to

override fun onSaveInstanceState(outState: Bundle) {
  super.onSaveInstanceState(outState)
  mapView.onSaveInstanceState(outState)
}

Noticed that with targeting Android 11 (R), nullabity of the former method was corrected to onSaveInstanceState(outState: Bundle, outPersistentState: PersistableBundle) and was giving me compilation issues. I have chaged the code to use the default OnSaveInstanceState, there is not specific reason to use the former for our use-case.

[Chaoba]

Should we add onSaveInstanceState for all test Activities?

[tobrun]

Should we add onSaveInstanceState for all test Activities?

sure, but not a high priority for this repository if you ask me