refactor: Standardize TensorFlowNET.Keras/Losses/*

fix: type converting errors when loading imdb dataset

feat: Support training of RNN and LSTM.

Fix my bad:

Bad handling between test_function and test_step_multi_inputs_function.

IModel.Dictionary<string, float> evaluate(NDArray, NDArray, ...) is now IModel.Dictionary<string, float> evaluate(Tensor, Tensor, ...)
Merge Model.Evaluate.test_step_multi_inputs_function(...) and Model.Evaluate.test_function(...)

Note: An internal function need to add an explicit cast in Tensor

feat: add rnn basic modules

Smooth implementation

Fix issue if data_handler.steps() > 1

build: add scripts to split large native library file.

fix: status null reference of base session.