Add a way to set keyframe request method on VideoReceiveStream

This patch adds a method for setting the keyframe request method
to VideoReceiveStream.

This code exists in the version that Mozilla is shipping, with a review
https://phabricator.services.mozilla.com/D105773 .

Bug: webrtc:13486
Change-Id: I7cc19dec95d6523368d73395319854bd8c2166f7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/240140
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Commit-Queue: Stefan Holmer <stefan@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35793}

modules/rtp_rtcp/include/rtp_rtcp_defines.h

@@ -103,6 +103,12 @@ enum RTCPPacketType : uint32_t {
   kRtcpXrTargetBitrate = 0x200000
 };
 
+enum class KeyFrameReqMethod : uint8_t {
+  kNone,     // Don't request keyframes.
+  kPliRtcp,  // Request keyframes through Picture Loss Indication.
+  kFirRtcp   // Request keyframes through Full Intra-frame Request.
+};
+
 enum RtxMode {
   kRtxOff = 0x0,
   kRtxRetransmitted = 0x1,     // Only send retransmissions over RTX.