Reland "Move api/rtp_headers.h to its own build target."

This is a reland of a67050debcb5a3461a452a7928d7aaea1562747e

Original change's description:
> Move api/rtp_headers.h to its own build target.
>
> Reduces dependencies on the libjingle_peerconnection_api target from
> lower-level code.
>
> Bug: None
> Change-Id: I98576fc718c396cc0f720c3770acd2b696b9df89
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/128565
> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> Commit-Queue: Niels Moller <nisse@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#27213}

Bug: None
Tbr: kwiberg@webrtc.org
Change-Id: If15b05957e50bb8f18a33c2ed1321e672311b626
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/127895
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27216}
diff --git a/video/BUILD.gn b/video/BUILD.gn
index a00f144..2e00d13 100644
--- a/video/BUILD.gn
+++ b/video/BUILD.gn
@@ -508,6 +508,7 @@
       "../api:fake_frame_encryptor",
       "../api:libjingle_peerconnection_api",
       "../api:mock_frame_decryptor",
+      "../api:rtp_headers",
       "../api:scoped_refptr",
       "../api:simulated_network_api",
       "../api/task_queue:default_task_queue_factory",