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}

sdk/objc/Framework/Classes/VideoToolbox/RTCVideoEncoderH264.mm

@@ -172,7 +172,7 @@ void compressionOutputCallback(void *encoder,
 // returned. The user must initialize the encoder with a resolution and
 // framerate conforming to the selected H264 level regardless.
 CFStringRef ExtractProfile(webrtc::SdpVideoFormat videoFormat) {
-  const rtc::Optional<webrtc::H264::ProfileLevelId> profile_level_id =
+  const absl::optional<webrtc::H264::ProfileLevelId> profile_level_id =
       webrtc::H264::ParseSdpProfileLevelId(videoFormat.parameters);
   RTC_DCHECK(profile_level_id);
   switch (profile_level_id->profile) {