Add support so requested resolution alignment also apply to scaled layers.

Bug: webrtc:11872
Change-Id: I7f904e2765330ee93270b66b0102ce57f336f9a0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/181883
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Commit-Queue: Åsa Persson <asapersson@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32146}

api/video_codecs/video_encoder_config.cc

@@ -43,6 +43,7 @@ std::string VideoStream::ToString() const {
   ss << ", num_temporal_layers: " << num_temporal_layers.value_or(1);
   ss << ", bitrate_priority: " << bitrate_priority.value_or(0);
   ss << ", active: " << active;
+  ss << ", scale_down_by: " << scale_resolution_down_by;
 
   return ss.str();
 }