Replace rtc::Optional with absl::optional in audio, call and video

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

This CL generated by running script with parameters 'audio call video':
#!/bin/bash
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: I02c5db956846a88a268a300ba086703a02d62e36
Reviewed-on: https://webrtc-review.googlesource.com/83722
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23628}
diff --git a/call/video_receive_stream.h b/call/video_receive_stream.h
index 3f01796..a5cd11a 100644
--- a/call/video_receive_stream.h
+++ b/call/video_receive_stream.h
@@ -82,7 +82,7 @@
     int render_delay_ms = 10;
     int64_t interframe_delay_max_ms = -1;
     uint32_t frames_decoded = 0;
-    rtc::Optional<uint64_t> qp_sum;
+    absl::optional<uint64_t> qp_sum;
 
     int current_payload_type = -1;
 
@@ -104,7 +104,7 @@
 
     // Timing frame info: all important timestamps for a full lifetime of a
     // single 'timing frame'.
-    rtc::Optional<webrtc::TimingFrameInfo> timing_frame_info;
+    absl::optional<webrtc::TimingFrameInfo> timing_frame_info;
   };
 
   struct Config {