Move sequence_number_utils.h to rtc_base/

Bug: webrtc:8440
Change-Id: I36e70da6ce70b95db7d3fce8b0013bff5c795bfc
Reviewed-on: https://webrtc-review.googlesource.com/14860
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20429}
diff --git a/video/BUILD.gn b/video/BUILD.gn
index 0833e52..8799a84 100644
--- a/video/BUILD.gn
+++ b/video/BUILD.gn
@@ -296,6 +296,7 @@
       "../modules/video_coding:webrtc_vp9",
       "../rtc_base:rtc_base_approved",
       "../rtc_base:rtc_base_tests_utils",
+      "../rtc_base:rtc_numerics",
       "../system_wrappers",
       "../system_wrappers:field_trial_default",
       "../system_wrappers:metrics_api",