Revert "Reland "Remove our stream << overloads from non-test build targets.""

This reverts commit d7ee72041f882c023c73e27a7436c626c4e43604.

Reason for revert: Broke downstream build which was using SdpAudioFormat operator<<

Original change's description:
> Reland "Remove our stream << overloads from non-test build targets."
> 
> This is a reland of c841d18d257ba8e4ed7d77d105e3c46006bb1e7e
> 
> Original change's description:
> > Remove our stream << overloads from non-test build targets.
> >
> > Most are removed entirely, but RtcErrorType, RtpTransceiverDirection, IPAddress and
> > SocketAddress are kept behind gtest's #ifdef UNIT_TEST.
> >
> > Bug: webrtc:8982
> > Change-Id: I36db19891e7d25aeacb08b9a08aa2b4004765e70
> > Reviewed-on: https://webrtc-review.googlesource.com/64143
> > Commit-Queue: Jonas Olsson <jonasolsson@webrtc.org>
> > Reviewed-by: Benjamin Wright <benwright@webrtc.org>
> > Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
> > Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> > Reviewed-by: Åsa Persson <asapersson@webrtc.org>
> > Cr-Commit-Position: refs/heads/master@{#22916}
> 
> TBR=deadbeef@webrtc.org,kwiberg@webrtc.org,asapersson@webrtc.org,jonasolsson@webrtc.org,benwright@webrtc.org
> 
> Bug: webrtc:8982
> Change-Id: Ibe08c6270e5e693eb661a6ce9e8f074b34ef8123
> Reviewed-on: https://webrtc-review.googlesource.com/71161
> Commit-Queue: Jonas Olsson <jonasolsson@webrtc.org>
> Reviewed-by: Jonas Olsson <jonasolsson@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#22949}

TBR=deadbeef@webrtc.org,kwiberg@webrtc.org,asapersson@webrtc.org,jonasolsson@webrtc.org,benwright@webrtc.org

Change-Id: I3c2b18ec2877d68a522ecbae7a2955c4eecf36df
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:8982
Reviewed-on: https://webrtc-review.googlesource.com/71446
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Commit-Queue: Taylor Brandstetter <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22963}
diff --git a/api/rtptransceiverinterface.h b/api/rtptransceiverinterface.h
index 7d2a1df..7805579 100644
--- a/api/rtptransceiverinterface.h
+++ b/api/rtptransceiverinterface.h
@@ -30,6 +30,9 @@
   kInactive
 };
 
+// This is provided as a debugging aid. The format of the output is unspecified.
+std::ostream& operator<<(std::ostream& os, RtpTransceiverDirection direction);
+
 // Structure for initializing an RtpTransceiver in a call to
 // PeerConnectionInterface::AddTransceiver.
 // https://w3c.github.io/webrtc-pc/#dom-rtcrtptransceiverinit