Pass datachannel priority in DC open messages

This adds priority to the API configuration of datachannels,
and passes the value in the OPEN message.

It does not yet influence SCTP prioritization of messages.

Bug: chromium:1083227
Change-Id: I46ddd1eefa0e3d07c959383788b9e80fcbfa38d6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/175107
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Taylor <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31287}

api/rtp_parameters.h

@@ -20,6 +20,7 @@
 #include "absl/strings/string_view.h"
 #include "absl/types/optional.h"
 #include "api/media_types.h"
+#include "api/priority.h"
 #include "api/rtp_transceiver_direction.h"
 #include "rtc_base/system/rtc_export.h"
 
@@ -93,14 +94,6 @@ enum class DegradationPreference {
 
 RTC_EXPORT extern const double kDefaultBitratePriority;
 
-// GENERATED_JAVA_ENUM_PACKAGE: org.webrtc
-enum class Priority {
-  kVeryLow,
-  kLow,
-  kMedium,
-  kHigh,
-};
-
 struct RTC_EXPORT RtcpFeedback {
   RtcpFeedbackType type = RtcpFeedbackType::CCM;