Make the experimental_new_quantizer flag to be public

PiperOrigin-RevId: 351421198

Author: liufengdb

tensorflow_model_optimization/python/examples/quantization/keras/mnist_cnn_cont_quant.py

@@ -134,7 +134,7 @@ def calibration_gen():
   converter = tf.lite.TFLiteConverter.from_keras_model(model)
 
 converter.representative_dataset = calibration_gen
-converter._experimental_new_quantizer = True  # pylint: disable=protected-access
+converter.experimental_new_quantizer = True
 converter.target_spec.supported_ops = [
     tf.lite.OpsSet.TFLITE_BUILTINS_INT8
 ]  # to enable post-training quantization with the representative dataset