Move EncoderStreamFactory into own file

This cl/ is a NOP refactoring,
moving the EncoderStreamFactory from within webrtc_video_engine.cc
into own file in video/. simulcast.cc is collateral.

Bug: webrtc:14451
Change-Id: Ia69b9241d8cd8a12be6628d887701f2e244c07cc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/276861
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Commit-Queue: Jonas Oreland <jonaso@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38224}

modules/video_coding/BUILD.gn

@@ -989,6 +989,7 @@ if (rtc_include_tests) {
       "../../test:test_support",
       "../../test:video_test_common",
       "../../test:video_test_support",
+      "../../video/config:streams_config",
     ]
     absl_deps = [
       "//third_party/abseil-cpp/absl/strings:strings",

modules/video_coding/DEPS

@@ -19,5 +19,6 @@ specific_include_rules = {
   ".*test.*\.cc": [
      "+media/base",
      "+media/engine",
+     "+video/config",
   ],
 }

modules/video_coding/codecs/test/videocodec_test_fixture_impl.cc

@@ -46,7 +46,6 @@
 #include "api/video_codecs/video_encoder_factory_template_open_h264_adapter.h"
 #include "common_video/h264/h264_common.h"
 #include "media/base/media_constants.h"
-#include "media/engine/simulcast.h"
 #include "modules/video_coding/codecs/h264/include/h264_globals.h"
 #include "modules/video_coding/codecs/vp9/svc_config.h"
 #include "modules/video_coding/utility/ivf_file_writer.h"
@@ -61,6 +60,7 @@
 #include "test/testsupport/file_utils.h"
 #include "test/testsupport/frame_writer.h"
 #include "test/video_codec_settings.h"
+#include "video/config/simulcast.h"
 
 namespace webrtc {
 namespace test {