Update IWYU tool with a mapping file

Also apply IWYU to all .cc files in pc/, and correct BUILD file to match.
Note: Some files came out wrong when iwyu was applied. These are not included.

Bug: none
Change-Id: Ib5ea46b8fcc505414d0447cca7218ad3afc2e321
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/252280
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36064}

pc/peer_connection_integrationtest.cc

@@ -14,6 +14,7 @@
 #include <memory>
 #include <string>
 #include <tuple>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
@@ -86,6 +87,8 @@
 #include "rtc_base/time_utils.h"
 #include "rtc_base/virtual_socket_server.h"
 #include "system_wrappers/include/metrics.h"
+#include "test/gmock.h"
+#include "test/gtest.h"
 
 namespace webrtc {