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/PeerConnection/RTCRtpCodecParameters.mm b/sdk/objc/Framework/Classes/PeerConnection/RTCRtpCodecParameters.mm
index b6baee6..7951cee 100644
--- a/sdk/objc/Framework/Classes/PeerConnection/RTCRtpCodecParameters.mm
+++ b/sdk/objc/Framework/Classes/PeerConnection/RTCRtpCodecParameters.mm
@@ -93,10 +93,10 @@
     RTC_NOTREACHED();
   }
   if (_clockRate != nil) {
-    parameters.clock_rate = rtc::Optional<int>(_clockRate.intValue);
+    parameters.clock_rate = absl::optional<int>(_clockRate.intValue);
   }
   if (_numChannels != nil) {
-    parameters.num_channels = rtc::Optional<int>(_numChannels.intValue);
+    parameters.num_channels = absl::optional<int>(_numChannels.intValue);
   }
   for (NSString *paramKey in _parameters.allKeys) {
     std::string key = [NSString stdStringForString:paramKey];