Replace rtc::Optional with absl::optional in modules/audio processing

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_processing'

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: Id29f8de59dba704787c2c38a3d05c60827c181b0
Reviewed-on: https://webrtc-review.googlesource.com/83982
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23653}

modules/audio_processing/include/audio_processing.h

@@ -22,9 +22,9 @@
 #include <string.h>
 #include <vector>
 
+#include "absl/types/optional.h"
 #include "api/audio/echo_canceller3_config.h"
 #include "api/audio/echo_control.h"
-#include "api/optional.h"
 #include "modules/audio_processing/beamformer/array_util.h"
 #include "modules/audio_processing/include/audio_generator.h"
 #include "modules/audio_processing/include/audio_processing_statistics.h"