Move webrtc::CreatePeerConnectionFactory definition next to decl.

This CL moves webrtc::CreatePeerConnectionFactory definitions out of
pc:create_pc_factory and merges it with its declaration in the api/
directory.

In order to avoid circular dependencies a new build target is created:
* api:create_peerconnection_factory

Bug: webrtc:9862
Change-Id: Ie215c94460cba026f5bf7d11c9a5aa03792064af
Reviewed-on: https://webrtc-review.googlesource.com/c/111186
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25744}
diff --git a/sdk/BUILD.gn b/sdk/BUILD.gn
index cc8f0a2..4f67d18 100644
--- a/sdk/BUILD.gn
+++ b/sdk/BUILD.gn
@@ -8,8 +8,8 @@
 
 import("../webrtc.gni")
 if (is_ios) {
-  import("//build/config/ios/rules.gni")
   import("//build/config/ios/ios_sdk.gni")
+  import("//build/config/ios/rules.gni")
 }
 if (is_mac) {
   import("//build/config/mac/rules.gni")
@@ -910,6 +910,7 @@
         ":videorendereradapter_objc",
         ":videosource_objc",
         ":videotoolbox_objc",
+        "../api:create_peerconnection_factory",
         "../api:libjingle_peerconnection_api",
         "../api/audio_codecs:audio_codecs_api",
         "../api/audio_codecs:builtin_audio_decoder_factory",
@@ -923,7 +924,6 @@
         "../modules/audio_processing:api",
         "../modules/audio_processing:audio_processing",
         "../modules/video_coding:video_codec_interface",
-        "../pc:create_pc_factory",
         "../pc:peerconnection",
         "../rtc_base:checks",
         "../rtc_base:rtc_base",