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}
diff --git a/api/rtp_parameters.h b/api/rtp_parameters.h
index 77db960..4af0833 100644
--- a/api/rtp_parameters.h
+++ b/api/rtp_parameters.h
@@ -447,10 +447,7 @@
   absl::optional<int> min_bitrate_bps;
 
   // Specifies the maximum framerate in fps for video.
-  // TODO(asapersson): Different framerates are not supported per simulcast
-  // layer. If set, the maximum |max_framerate| is currently used.
-  // Not supported for screencast.
-  absl::optional<int> max_framerate;
+  absl::optional<double> max_framerate;
 
   // Specifies the number of temporal layers for video (if the feature is
   // supported by the codec implementation).