merge 2.10.x

review by @gkossakowski 


```patch
 -      var materializer = atPos(pos.focus)(gen.mkMethodCall(TagMaterializers(tagClass), List(tp), if (prefix != EmptyTree) List(prefix) else List()))
 +      val materializer = atPos(pos.focus)(gen.mkMethodCall(TagMaterializers(tagClass), List(tp), if (prefix != EmptyTree) List(prefix) else List()))
-       if (settings.XlogImplicits.value) println("materializing requested %s.%s[%s] using %s".format(pre, tagClass.name, tp, materializer))
+       if (settings.XlogImplicits.value) reporter.echo(pos, "materializing requested %s.%s[%s] using %s".format(pre, tagClass.name, tp, materializer))
```