Fork contrib's timeseries into the canned estimator folder and clean it up to...

Fork contrib's timeseries into the canned estimator folder and clean it up to only include LSTMAutoRegressor and its dependencies. After the fork, the following changes were made:

1. Imports are pointed to the new fork except for symbols that were removed during the next steps of the clean up (see below). tensorflow/.../estimator imports were changed to tensorflow_estimator/...

2. estimators.py had all its symbols removed except for LSTMAutoRegressor which is the one we want to keep.

3. ar_model.py had all its symbols removed except for LSTMPredictionModel and ARModel (which uses LSTMPredictionModel).

4. state_management.py had ChainingStateManager removed and as state_management_test.py only tests ChainingStateManager, that test file was removed.

5. math_utils.py had all its symbols removed except for InputStatisticsFromMiniBatch and replicate_state.

6. examples folder was removed. This will come back in some form (perhaps an updated docstring in estimators.py) before LSTMAutoRegressor is exported.

7. input_pipeline.py was removed. This is going to be replaced with a user supplied tf.data-backed input_fn. For now, tests point to contrib's input_pipeline.

8. Cleaned up the BUILD and __init__.py files. Fixed rules and removed stale tags.

PiperOrigin-RevId: 229654011