Rename api/stats_types.h to api/legacy_stats_types.h.

As to not break downstream projects, the old name api/stats_types.h is
kept around to help include api/legacy_stats_types.h. We can delete this
in a follow-up.

NOTRY=True

Bug: webrtc:14180
Change-Id: I270ca5e366ae36e324cbc9f982bbb066ab92d203
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/283081
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38610}
diff --git a/pc/peer_connection_message_handler.cc b/pc/peer_connection_message_handler.cc
index 2d674aa..8ddedde 100644
--- a/pc/peer_connection_message_handler.cc
+++ b/pc/peer_connection_message_handler.cc
@@ -13,11 +13,11 @@
 #include <utility>
 
 #include "api/jsep.h"
+#include "api/legacy_stats_types.h"
 #include "api/media_stream_interface.h"
 #include "api/peer_connection_interface.h"
 #include "api/scoped_refptr.h"
 #include "api/sequence_checker.h"
-#include "api/stats_types.h"
 #include "api/task_queue/pending_task_safety_flag.h"
 #include "pc/legacy_stats_collector_interface.h"
 #include "rtc_base/checks.h"