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}
diff --git a/audio/BUILD.gn b/audio/BUILD.gn
index ce6525e..4fdb1f6 100644
--- a/audio/BUILD.gn
+++ b/audio/BUILD.gn
@@ -40,6 +40,7 @@
   deps = [
     "../api:array_view",
     "../api:call_api",
+    "../api:function_view",
     "../api:libjingle_peerconnection_api",
     "../api:rtp_headers",
     "../api:scoped_refptr",