Method EncoderLayerStack

Clean EncoderLayerStack with minimal layer nesting. E.g:: encoder/ layer_000/ ln/w/ scale self_attention/w/ wq wk wv wo layer_001/ ... will be constructed with:: builder.

(self,
                        name,
                        sub_layers,
                        num=1,
                        use_repeat_layer=False,
                        spmd_pipeline_stages=1,
                        spmd_pipeline_microbatches=None)