Introcuce RTCError(const T&) constructor.

This CL is spawned from [1] and it introduces RTCError(const T&) in
order to remove an unneeded std::move.

[1] - https://webrtc-review.googlesource.com/c/src/+/120350

Bug: webrtc:10252
Change-Id: Ibd5aa1c901fd920549e9437908178c786019a328
Reviewed-on: https://webrtc-review.googlesource.com/c/120560
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26468}

api/rtc_error.h

@@ -220,6 +220,7 @@ class RTCErrorOr {
   // NOTE: Not explicit - we want to use RTCErrorOr<T> as a return type
   // so it is convenient and sensible to be able to do 'return T()'
   // when the return type is RTCErrorOr<T>.
+  RTCErrorOr(const T& value) : value_(value) {}        // NOLINT
   RTCErrorOr(T&& value) : value_(std::move(value)) {}  // NOLINT
 
   // Delete the copy constructor and assignment operator; there aren't any use

pc/peer_connection.cc

@@ -6016,7 +6016,7 @@ RTCErrorOr<const cricket::ContentGroup*> PeerConnection::GetEarlyBundleGroup(
                            "has no BUNDLE group");
     }
   }
-  return std::move(bundle_group);
+  return bundle_group;
 }
 
 RTCError PeerConnection::CreateChannels(const SessionDescription& desc) {