Replace rtc::Optional with absl::optional

This is a no-op change because rtc::Optional is an alias to absl::optional

This CL generated by running script from modules with parameters
'pacing video_coding congestion_controller remote_bitrate_estimator':

find $@ -type f \( -name \*.h -o -name \*.cc \) \
-exec sed -i 's|rtc::Optional|absl::optional|g' {} \+ \
-exec sed -i 's|rtc::nullopt|absl::nullopt|g' {} \+ \
-exec sed -i 's|#include "api/optional.h"|#include "absl/types/optional.h"|' {} \+

find $@ -type f -name BUILD.gn \
-exec sed -r -i 's|"(../)*api:optional"|"//third_party/abseil-cpp/absl/types:optional"|' {} \+;

git cl format

Bug: webrtc:9078
Change-Id: I8ea501d7f1ee36e8d8cd3ed37e6b763c7fe29118
Reviewed-on: https://webrtc-review.googlesource.com/83900
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23640}
diff --git a/modules/video_coding/packet_buffer.h b/modules/video_coding/packet_buffer.h
index 9b1228d..51d2782 100644
--- a/modules/video_coding/packet_buffer.h
+++ b/modules/video_coding/packet_buffer.h
@@ -58,8 +58,8 @@
   void PaddingReceived(uint16_t seq_num);
 
   // Timestamp (not RTP timestamp) of the last received packet/keyframe packet.
-  rtc::Optional<int64_t> LastReceivedPacketMs() const;
-  rtc::Optional<int64_t> LastReceivedKeyframePacketMs() const;
+  absl::optional<int64_t> LastReceivedPacketMs() const;
+  absl::optional<int64_t> LastReceivedKeyframePacketMs() const;
 
   // Returns number of different frames seen in the packet buffer
   int GetUniqueFramesSeen() const;
@@ -159,13 +159,13 @@
   OnReceivedFrameCallback* const received_frame_callback_;
 
   // Timestamp (not RTP timestamp) of the last received packet/keyframe packet.
-  rtc::Optional<int64_t> last_received_packet_ms_ RTC_GUARDED_BY(crit_);
-  rtc::Optional<int64_t> last_received_keyframe_packet_ms_
+  absl::optional<int64_t> last_received_packet_ms_ RTC_GUARDED_BY(crit_);
+  absl::optional<int64_t> last_received_keyframe_packet_ms_
       RTC_GUARDED_BY(crit_);
 
   int unique_frames_seen_ RTC_GUARDED_BY(crit_);
 
-  rtc::Optional<uint16_t> newest_inserted_seq_num_ RTC_GUARDED_BY(crit_);
+  absl::optional<uint16_t> newest_inserted_seq_num_ RTC_GUARDED_BY(crit_);
   std::set<uint16_t, DescendingSeqNumComp<uint16_t>> missing_packets_
       RTC_GUARDED_BY(crit_);