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/api/DEPS b/api/DEPS
index 5f01204..bcfd705 100644
--- a/api/DEPS
+++ b/api/DEPS
@@ -182,7 +182,7 @@
     "+rtc_base/ref_count.h",
   ],
 
-  "stats_types\.h": [
+  "legacy_stats_types\.h": [
     "+rtc_base/ref_count.h",
     "+rtc_base/thread_checker.h",
   ],