Fix output shape of TransformerEncoder
Fix output shape of TransformerEncoder

PiperOrigin-RevId: 169345762

rsepassi/tensor2tensor,waterblue13/tensor2tensor,vthorsteinsson/tensor2tensor,vthorsteinsson/tensor2tensor,vthorsteinsson/tensor2tensor,tensorflow/tensor2tensor,vthorsteinsson/tensor2tensor,rsepassi/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor,waterblue13/tensor2tensor,waterblue13/tensor2tensor,tensorflow/tensor2tensor,rsepassi/tensor2tensor,rsepassi/tensor2tensor,tensorflow/tensor2tensor