title: How to combine and filter two dart Streams
body: <p>I am using flutter_blue for a flutter Application using bluetooth.</p>
  
  <p>flutter_blue presents me with two streams:
     FlutterBlue.instance.connectedDevices
     FlutterBlue.instance.scanResults</p>
  
  <p>I would like to combine those two streams into one and apply a filter.</p>
  
  <p>Googling around I get references to rxdart but still,, I cant get it to work.
  Help please :) </p>