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

This reverts commit c841d18d257ba8e4ed7d77d105e3c46006bb1e7e.

Reason for revert: Breaks internal tests

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

Change-Id: Ia3a36cdbdb2a9648a2bce23c314e539124dc9e0d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:8982
Reviewed-on: https://webrtc-review.googlesource.com/70640
Reviewed-by: Jonas Olsson <jonasolsson@webrtc.org>
Commit-Queue: Jonas Olsson <jonasolsson@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22920}

api/rtptransceiverinterface.h

@@ -30,6 +30,9 @@ enum class RtpTransceiverDirection {
   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