Fix circular dependencies in webrtc_common.

One reason for the circular deps is that common_types.h is a
historical dumping ground for various structs and defines that
are believed to be generally useful. I tried moving things out
that did not appear to be used downstream (StreamCounters,
RtpCounters etc) and moved the things that seemed used
(RtpHeader + supporting structs) to a new file api/rtp_headers.h.
This makes their place in the api more clear while moving out
the things that don't belong in the API in the first place.

I had to extract out typedefs.h from webrtc_common to resolve
another circular dependency. I believe checks includes typedefs,
but common depends on checks.

Bug: webrtc:7745
Change-Id: I725d49616b1ec0cdc8b74be7c078f7a4d46f084b
Reviewed-on: https://webrtc-review.googlesource.com/33001
Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21295}
diff --git a/modules/BUILD.gn b/modules/BUILD.gn
index 2c1a042..33394f4 100644
--- a/modules/BUILD.gn
+++ b/modules/BUILD.gn
@@ -34,6 +34,7 @@
   ]
   deps = [
     "..:webrtc_common",
+    "../:typedefs",
     "../api:optional",
   ]
 }
@@ -46,9 +47,12 @@
   deps = [
     ":module_api_public",
     "..:webrtc_common",
+    "../:typedefs",
+    "../api:libjingle_peerconnection_api",
     "../api:optional",
     "../api:video_frame_api",
     "../api:video_frame_api_i420",
+    "../rtc_base:deprecation",
     "../rtc_base:rtc_base_approved",
     "video_coding:codec_globals_headers",
   ]