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/generic_decoder.cc b/modules/video_coding/generic_decoder.cc
index 1d1c2fd..580bfc9 100644
--- a/modules/video_coding/generic_decoder.cc
+++ b/modules/video_coding/generic_decoder.cc
@@ -57,15 +57,15 @@
 int32_t VCMDecodedFrameCallback::Decoded(VideoFrame& decodedImage,
                                          int64_t decode_time_ms) {
   Decoded(decodedImage,
-          decode_time_ms >= 0 ? rtc::Optional<int32_t>(decode_time_ms)
-                              : rtc::nullopt,
-          rtc::nullopt);
+          decode_time_ms >= 0 ? absl::optional<int32_t>(decode_time_ms)
+                              : absl::nullopt,
+          absl::nullopt);
   return WEBRTC_VIDEO_CODEC_OK;
 }
 
 void VCMDecodedFrameCallback::Decoded(VideoFrame& decodedImage,
-                                      rtc::Optional<int32_t> decode_time_ms,
-                                      rtc::Optional<uint8_t> qp) {
+                                      absl::optional<int32_t> decode_time_ms,
+                                      absl::optional<uint8_t> qp) {
   RTC_DCHECK(_receiveCallback) << "Callback must not be null at this point";
   TRACE_EVENT_INSTANT1("webrtc", "VCMDecodedFrameCallback::Decoded",
                        "timestamp", decodedImage.timestamp());