Move rtc::FunctionView to the public API

Bug: webrtc:10138
Change-Id: Icc25a2a277a9608701aaddd546882366739991ca
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/127898
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27227}

logging/rtc_event_log/rtc_event_processor.h

@@ -18,8 +18,8 @@
 #include <vector>
 
 #include "absl/memory/memory.h"
+#include "api/function_view.h"
 #include "rtc_base/checks.h"
-#include "rtc_base/function_view.h"
 
 namespace webrtc {