Replace rtc::Optional with absl::optional in modules/audio_coding

This is a no-op change because rtc::Optional is an alias to absl::optional

This CL generated by running script with parameter 'modules/audio_coding'

find $@ -type f \( -name \*.h -o -name \*.cc \) \
-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: Ic980ee605148fdb160666d4aa03cc87175e48fe8
Reviewed-on: https://webrtc-review.googlesource.com/84130
Reviewed-by: Oskar Sundbom <ossu@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23659}

modules/audio_coding/neteq/neteq_decoder_enum.h

@@ -11,8 +11,8 @@
 #ifndef MODULES_AUDIO_CODING_NETEQ_NETEQ_DECODER_ENUM_H_
 #define MODULES_AUDIO_CODING_NETEQ_NETEQ_DECODER_ENUM_H_
 
+#include "absl/types/optional.h"
 #include "api/audio_codecs/audio_format.h"
-#include "api/optional.h"
 
 namespace webrtc {
 
@@ -49,7 +49,7 @@ enum class NetEqDecoder {
   kDecoderOpus_2ch,
 };
 
-rtc::Optional<SdpAudioFormat> NetEqDecoderToSdpAudioFormat(NetEqDecoder nd);
+absl::optional<SdpAudioFormat> NetEqDecoderToSdpAudioFormat(NetEqDecoder nd);
 
 }  // namespace webrtc