Reland "Implement RtpParameters.transaction_id for PC RtpSenderInterface"

This is a reland of 5faf36ef3c582350fba5ef97a3549e440d81a283
The issue in Chrome has been fixed and this should be safe to reland.

TBR=deadbeef

Original change's description:
> Implement RtpParameters.transaction_id for PC RtpSenderInterface
>
> The transaction_id field should be refreshed for every getParameters()
> call and checked at each setParameters() call.
> This also checks that getParameters() was ever called to return a proper
> error code.
>
> Bug: webrtc:7580
> Change-Id: I6c6fe289542e486fc422cdc61577982b0529d4c1
> Reviewed-on: https://webrtc-review.googlesource.com/70820
> Commit-Queue: Florent Castelli <orphis@webrtc.org>
> Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
> Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
> Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
> Reviewed-by: Steve Anton <steveanton@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#23120}

Bug: webrtc:7580
Change-Id: Iabd41fb21afdf452c039d5513824ae334f8d1d3f
Reviewed-on: https://webrtc-review.googlesource.com/76980
Commit-Queue: Florent Castelli <orphis@webrtc.org>
Reviewed-by: Florent Castelli <orphis@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23247}

sdk/objc/Framework/Headers/WebRTC/RTCRtpParameters.h

@@ -19,6 +19,9 @@ NS_ASSUME_NONNULL_BEGIN
 RTC_EXPORT
 @interface RTCRtpParameters : NSObject
 
+/** A unique identifier for the last set of parameters applied. */
+@property(nonatomic, copy) NSString *transactionId;
+
 /** The currently active encodings in the order of preference. */
 @property(nonatomic, copy) NSArray<RTCRtpEncodingParameters *> *encodings;