Replace rtc::Optional with absl::optional in audio, call and video

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

This CL generated by running script with parameters 'audio call video':
#!/bin/bash
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: I02c5db956846a88a268a300ba086703a02d62e36
Reviewed-on: https://webrtc-review.googlesource.com/83722
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23628}
diff --git a/video/video_stream_decoder_impl.h b/video/video_stream_decoder_impl.h
index d4de7b6..cd1f953 100644
--- a/video/video_stream_decoder_impl.h
+++ b/video/video_stream_decoder_impl.h
@@ -15,7 +15,7 @@
 #include <memory>
 #include <utility>
 
-#include "api/optional.h"
+#include "absl/types/optional.h"
 #include "api/video/video_stream_decoder.h"
 #include "modules/video_coding/frame_buffer2.h"
 #include "modules/video_coding/jitter_estimator.h"
@@ -64,8 +64,8 @@
   int32_t Decoded(VideoFrame& decodedImage) override;
   int32_t Decoded(VideoFrame& decodedImage, int64_t decode_time_ms) override;
   void Decoded(VideoFrame& decodedImage,
-               rtc::Optional<int32_t> decode_time_ms,
-               rtc::Optional<uint8_t> qp) override;
+               absl::optional<int32_t> decode_time_ms,
+               absl::optional<uint8_t> qp) override;
 
   VideoStreamDecoder::Callbacks* const callbacks_
       RTC_PT_GUARDED_BY(bookkeeping_queue_);
@@ -83,7 +83,7 @@
   VCMTiming timing_;
   video_coding::FrameBuffer frame_buffer_;
   video_coding::VideoLayerFrameId last_continuous_id_;
-  rtc::Optional<int> current_payload_type_;
+  absl::optional<int> current_payload_type_;
   std::unique_ptr<VideoDecoder> decoder_;
 
   // Some decoders are pipelined so it is not sufficient to save frame info