Splitting quantize_tensor and quantize_input

[jchen351]

Description: Describe your changes.
Splitting quantize_tensor and quantize_input into quantize_activation_tensor, quantize_weight_tensor, quantize_activation and quantize_weight
Motivation and Context
This will reduce the naming confusion

[chenfucn]

def is_input_a_weight(self, input_name):

Change this to is_input_an_initializer to be consistent with rest of the name change?

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Refers to: onnxruntime/python/tools/quantization/onnx_quantizer.py:292 in 5ab6073. [](commit_id = 5ab6073, deletion_comment = False)

[chenfucn]

It appears to me that we used to use 'initializer' as a synonym for 'weight', and this change is aim at changing that? It would be great if we can have explanation of this in comments.

[yufenglee]