Standardize keras symbol imports

[jbischof]

The new standard for importing Keras is from tensorflow import keras. Most of the guides and examples on keras.io do this, but our symbol imports are all over the place including:

keras.foo()
tf.keras.foo()
tensorflow.keras.foo()

Let's standardize on keras.foo(). Like #1181, we can directly modify both generated and original files with a simple find-and-replace since it would be too much work to regenerate everything. The main caveat is checking that each script has the topline import from tensorflow import keras, which it should!

[mattdangerw]

We made a deliberate call to always import keras and keras_nlp as top-levels for examples using KerasNLP. https://github.com/keras-team/keras-nlp/blob/master/STYLE_GUIDE.md#import-keras-and-keras_nlp-as-top-level-objects

I'm not sure if we want that style universally, but for domain packages the style is useful.

[sachinprasadhs]

Since we have direct import of Keras now, do you find this request still relevant now?

[jbischof]

Nope, thank you!

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