Android: restore SystemUiVisibility state

System UI visibility is saved under onSaveInstanceState()
but never restored under onRestoreInstanceState().

Task-number: QTBUG-118077
Change-Id: Ic9956a4aca9e0b9bb5fefa37d7229dd0d52c7344
Reviewed-by: Tinja Paavoseppä <tinja.paavoseppa@qt.io>

src/android/jar/src/org/qtproject/qt/android/QtActivityBase.java

@@ -256,6 +256,8 @@ public class QtActivityBase extends Activity
     {
         super.onRestoreInstanceState(savedInstanceState);
         QtNative.setStarted(savedInstanceState.getBoolean("Started"));
+        int savedSystemUiVisibility = savedInstanceState.getInt("SystemUiVisibility");
+        m_delegate.displayManager().setSystemUiVisibility(this, savedSystemUiVisibility);
         // FIXME restore all surfaces
     }