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 passing top level directories except rtc_base and api

find $@ -type f \( -name \*.h -o -name \*.cc -o -name \*.mm \) \
-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: I9465c172e65ba6e6ed4e4fdc35b0b265038d6f71
Reviewed-on: https://webrtc-review.googlesource.com/84584
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23697}
diff --git a/common_video/video_render_frames.h b/common_video/video_render_frames.h
index af254f2..31a4634 100644
--- a/common_video/video_render_frames.h
+++ b/common_video/video_render_frames.h
@@ -15,7 +15,7 @@
 
 #include <list>
 
-#include "api/optional.h"
+#include "absl/types/optional.h"
 #include "api/video/video_frame.h"
 
 namespace webrtc {
@@ -30,7 +30,7 @@
   int32_t AddFrame(VideoFrame&& new_frame);
 
   // Get a frame for rendering, or false if it's not time to render.
-  rtc::Optional<VideoFrame> FrameToRender();
+  absl::optional<VideoFrame> FrameToRender();
 
   // Returns the number of ms to next frame to render
   uint32_t TimeToNextFrameRelease();