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/timing.h b/modules/video_coding/timing.h
index 8c04ce2..08ec193 100644
--- a/modules/video_coding/timing.h
+++ b/modules/video_coding/timing.h
@@ -95,7 +95,7 @@
                           int* render_delay_ms) const;
 
   void SetTimingFrameInfo(const TimingFrameInfo& info);
-  rtc::Optional<TimingFrameInfo> GetTimingFrameInfo();
+  absl::optional<TimingFrameInfo> GetTimingFrameInfo();
 
   enum { kDefaultRenderDelayMs = 10 };
   enum { kDelayMaxChangeMsPerS = 100 };
@@ -124,7 +124,7 @@
   int current_delay_ms_ RTC_GUARDED_BY(crit_sect_);
   int last_decode_ms_ RTC_GUARDED_BY(crit_sect_);
   uint32_t prev_frame_timestamp_ RTC_GUARDED_BY(crit_sect_);
-  rtc::Optional<TimingFrameInfo> timing_frame_info_ RTC_GUARDED_BY(crit_sect_);
+  absl::optional<TimingFrameInfo> timing_frame_info_ RTC_GUARDED_BY(crit_sect_);
   size_t num_decoded_frames_ RTC_GUARDED_BY(crit_sect_);
 };
 }  // namespace webrtc