Copy raw data when emitting dense attributes in BEF.
Copy raw data when emitting dense attributes in BEF.

Previously it was creating a new attribute for each element when iterating through the MLIR dense attributes, which was very expensive. This CL also adds a few benchmarks for emitting dense attributes.

PiperOrigin-RevId: 369576269

tensorflow/runtime,tensorflow/runtime,tensorflow/runtime,tensorflow/runtime