THRIFT-5326: Expand TException interface in go library

Client: go

Add TExceptionType enum type, and add

    TExceptionType() TExceptionType

function to TException definition.

Also make TProtocolException unwrap-able.
diff --git a/lib/go/test/tests/thrifttest_handler.go b/lib/go/test/tests/thrifttest_handler.go
index 31b9ee2..7b115ec 100644
--- a/lib/go/test/tests/thrifttest_handler.go
+++ b/lib/go/test/tests/thrifttest_handler.go
@@ -179,7 +179,7 @@
 		x.Message = arg
 		return x
 	} else if arg == "TException" {
-		return thrift.TException(errors.New(arg))
+		return thrift.WrapTException(errors.New(arg))
 	} else {
 		return nil
 	}