[Cleanup] Add missing #include. Remove useless ones. IWYU part 2.

This is a follow-up to
https://webrtc-review.googlesource.com/c/src/+/106280.
This time the whole code base is covered.
Some files may have not been fixed though, whenever the IWYU tool
was breaking the build.

Bug: webrtc:8311
Change-Id: I2c31f552a87e887d33931d46e87b6208b1e483ef
Reviewed-on: https://webrtc-review.googlesource.com/c/111965
Commit-Queue: Yves Gerey <yvesg@google.com>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25830}
diff --git a/rtc_base/nat_unittest.cc b/rtc_base/nat_unittest.cc
index ee94427..8031dff 100644
--- a/rtc_base/nat_unittest.cc
+++ b/rtc_base/nat_unittest.cc
@@ -8,21 +8,34 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+#include <string.h>
 #include <algorithm>
 #include <memory>
 #include <string>
+#include <vector>
 
 #include "absl/memory/memory.h"
+#include "rtc_base/asyncpacketsocket.h"
+#include "rtc_base/asyncsocket.h"
 #include "rtc_base/asynctcpsocket.h"
+#include "rtc_base/asyncudpsocket.h"
 #include "rtc_base/gunit.h"
+#include "rtc_base/ipaddress.h"
 #include "rtc_base/logging.h"
 #include "rtc_base/natserver.h"
 #include "rtc_base/natsocketfactory.h"
+#include "rtc_base/nattypes.h"
 #include "rtc_base/nethelpers.h"
 #include "rtc_base/network.h"
 #include "rtc_base/physicalsocketserver.h"
+#include "rtc_base/socketaddress.h"
+#include "rtc_base/socketfactory.h"
+#include "rtc_base/socketserver.h"
 #include "rtc_base/testclient.h"
+#include "rtc_base/third_party/sigslot/sigslot.h"
+#include "rtc_base/thread.h"
 #include "rtc_base/virtualsocketserver.h"
+#include "test/gtest.h"
 
 using namespace rtc;