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}

pc/peer_connection_wrapper.cc

diff --git a/pc/peer_connection_wrapper.cc b/pc/peer_connection_wrapper.cc
index 6bfb59f..74089f6 100644
--- a/pc/peer_connection_wrapper.cc
+++ b/pc/peer_connection_wrapper.cc
@@ -16,11 +16,11 @@
 #include <utility>
 #include <vector>
 
+#include "api/function_view.h"
 #include "api/set_remote_description_observer_interface.h"
 #include "pc/sdp_utils.h"
 #include "pc/test/fake_video_track_source.h"
 #include "rtc_base/checks.h"
-#include "rtc_base/function_view.h"
 #include "rtc_base/gunit.h"
 #include "rtc_base/logging.h"
 #include "rtc_base/ref_counted_object.h"