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/sdk/objc/Framework/Classes/Video/RTCDefaultShader.mm b/sdk/objc/Framework/Classes/Video/RTCDefaultShader.mm
index 3caf144..c5fbde1 100644
--- a/sdk/objc/Framework/Classes/Video/RTCDefaultShader.mm
+++ b/sdk/objc/Framework/Classes/Video/RTCDefaultShader.mm
@@ -20,7 +20,7 @@
 #import "RTCShader.h"
 #import "WebRTC/RTCLogging.h"
 
-#include "api/optional.h"
+#include "absl/types/optional.h"
 
 static const int kYTextureUnit = 0;
 static const int kUTextureUnit = 1;
@@ -73,7 +73,7 @@
   GLuint _vertexBuffer;
   GLuint _vertexArray;
   // Store current rotation and only upload new vertex data when rotation changes.
-  rtc::Optional<RTCVideoRotation> _currentRotation;
+  absl::optional<RTCVideoRotation> _currentRotation;
 
   GLuint _i420Program;
   GLuint _nv12Program;
@@ -144,7 +144,7 @@
 #endif
   glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
   if (!_currentRotation || rotation != *_currentRotation) {
-    _currentRotation = rtc::Optional<RTCVideoRotation>(rotation);
+    _currentRotation = absl::optional<RTCVideoRotation>(rotation);
     RTCSetVertexData(*_currentRotation);
   }
   return YES;