Updated Tensorflow.Net to 0.70.2 with Tensorflow 2.7.0.

[Crichen]

Fixes #7471

NumSharp replaced with Tensorflow.NumPy. TensorShape replaced with Shape, Shape object has dimensions as 64 bit long, check added for casting to 32 bit int alsoTensor constructor using SafeTensorHandle/DangerousGetHandle and TF_DataType not required when casting.

Added StringTensorFactory to wrap addition tensorflow.dll methods required to create Tensors from string based input.

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