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/PeerConnection/RTCConfiguration.mm

@@ -171,8 +171,8 @@
   // Generate non-default certificate.
   if (keyType != rtc::KT_DEFAULT) {
     rtc::scoped_refptr<rtc::RTCCertificate> certificate =
-        rtc::RTCCertificateGenerator::GenerateCertificate(
-            rtc::KeyParams(keyType), rtc::Optional<uint64_t>());
+        rtc::RTCCertificateGenerator::GenerateCertificate(rtc::KeyParams(keyType),
+                                                          absl::optional<uint64_t>());
     if (!certificate) {
       RTCLogError(@"Failed to generate certificate.");
       return nullptr;
@@ -184,14 +184,13 @@
   nativeConfig->presume_writable_when_fully_relayed =
       _shouldPresumeWritableWhenFullyRelayed ? true : false;
   if (_iceCheckMinInterval != nil) {
-    nativeConfig->ice_check_min_interval =
-        rtc::Optional<int>(_iceCheckMinInterval.intValue);
+    nativeConfig->ice_check_min_interval = absl::optional<int>(_iceCheckMinInterval.intValue);
   }
   if (_iceRegatherIntervalRange != nil) {
     std::unique_ptr<rtc::IntervalRange> nativeIntervalRange(
         _iceRegatherIntervalRange.nativeIntervalRange);
     nativeConfig->ice_regather_interval_range =
-        rtc::Optional<rtc::IntervalRange>(*nativeIntervalRange);
+        absl::optional<rtc::IntervalRange>(*nativeIntervalRange);
   }
   nativeConfig->sdp_semantics = [[self class] nativeSdpSemanticsForSdpSemantics:_sdpSemantics];
   if (_turnCustomizer) {