Add AbsoluteCaptureTime to RtpPacketInfo.

This change stores the optional `AbsoluteCaptureTime` header extension in `RtpPacketInfo` so that we later can consume it in `SourceTracker`.

Bug: webrtc:10739
Change-Id: I975e8863117fcda134535cd49ad71079a7ff38ec
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/148068
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Chen Xing <chxg@google.com>
Cr-Commit-Position: refs/heads/master@{#28790}

modules/audio_coding/neteq/red_payload_splitter.cc

@@ -123,6 +123,7 @@ bool RedPayloadSplitter::SplitRed(PacketList* packet_list) {
             /*csrcs=*/std::vector<uint32_t>(),
             /*rtp_timestamp=*/new_packet.timestamp,
             /*audio_level=*/absl::nullopt,
+            /*absolute_capture_time=*/absl::nullopt,
             /*receive_time_ms=*/red_packet.packet_info.receive_time_ms());
         new_packets.push_front(std::move(new_packet));
         payload_ptr += payload_length;