Add support for RtpEncodingParameters::max_framerate

This adds the framework support for the max_framerate parameter.
It doesn't implement it in any encoder yet.

Bug: webrtc:11117
Change-Id: I329624cc0205c828498d3623a2e13dd3f97e1629
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/160184
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Commit-Queue: Florent Castelli <orphis@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29907}

api/video_codecs/video_codec.cc

@@ -48,6 +48,7 @@ bool VideoCodecH264::operator==(const VideoCodecH264& other) const {
 
 bool SpatialLayer::operator==(const SpatialLayer& other) const {
   return (width == other.width && height == other.height &&
+          maxFramerate == other.maxFramerate &&
           numberOfTemporalLayers == other.numberOfTemporalLayers &&
           maxBitrate == other.maxBitrate &&
           targetBitrate == other.targetBitrate &&