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/aec3/echo_remover.cc

@@ -68,14 +68,14 @@ class EchoRemoverImpl final : public EchoRemover {
   // signal.
   void ProcessCapture(const EchoPathVariability& echo_path_variability,
                       bool capture_signal_saturation,
-                      const rtc::Optional<DelayEstimate>& external_delay,
+                      const absl::optional<DelayEstimate>& external_delay,
                       RenderBuffer* render_buffer,
                       std::vector<std::vector<float>>* capture) override;
 
   // Returns the internal delay estimate in blocks.
-  rtc::Optional<int> Delay() const override {
+  absl::optional<int> Delay() const override {
     // TODO(peah): Remove or reactivate this functionality.
-    return rtc::nullopt;
+    return absl::nullopt;
   }
 
   // Updates the status on whether echo leakage is detected in the output of the
@@ -143,7 +143,7 @@ void EchoRemoverImpl::GetMetrics(EchoControl::Metrics* metrics) const {
 void EchoRemoverImpl::ProcessCapture(
     const EchoPathVariability& echo_path_variability,
     bool capture_signal_saturation,
-    const rtc::Optional<DelayEstimate>& external_delay,
+    const absl::optional<DelayEstimate>& external_delay,
     RenderBuffer* render_buffer,
     std::vector<std::vector<float>>* capture) {
   const std::vector<std::vector<float>>& x = render_buffer->Block(0);