Moves QuicTag typedefs, and QuicTag utility methods to quic_tag.{h,cc}. No behavior change.

net/quic/core/quic_versions.cc

Index: net/quic/core/quic_versions.cc
diff --git a/net/quic/core/quic_versions.cc b/net/quic/core/quic_versions.cc
index d6db947b3159c62bc0f94f6b6f352eaf3ebbba5a..ff8c2d5ba24dc1fc475f8900465f1989cd5b8a99 100644
--- a/net/quic/core/quic_versions.cc
+++ b/net/quic/core/quic_versions.cc
@@ -7,6 +7,7 @@
 #include "base/memory/ptr_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "net/quic/core/quic_flags.h"
+#include "net/quic/core/quic_tag.h"
 #include "net/quic/core/quic_types.h"
 #include "net/quic/core/quic_utils.h"
 
@@ -83,8 +84,7 @@ QuicVersion QuicTagToQuicVersion(const QuicTag version_tag) {
     }
   }
   // Reading from the client so this should not be considered an ERROR.
-  DVLOG(1) << "Unsupported QuicTag version: "
-           << QuicUtils::TagToString(version_tag);
+  DVLOG(1) << "Unsupported QuicTag version: " << QuicTagToString(version_tag);
   return QUIC_VERSION_UNSUPPORTED;
 }