Major Features and Improvements
* Updated TF version to 2.12.0.
* Relaxed runtime type checks on `tff.learning.templates.LearningProcess` to
allow non-sequence CLIENTS arguments.
* `tff.simulation.compose_dataset_computation_with_learning_process` now
returns a `tff.learning.templates.LearningProcess`.
* Updated the `tff.program.FederatedDataSourceIterator`s so that they can be
serialized.
Breaking Changes
* Deleted the `forward_pass` attribute from the `FunctionalModel` interface.
* Removed `from_keras_model`, `MetricsFinalizersType`, `BatchOutput`, `Model`,
and `ModelWeights` symbols from the `tff.learning` package. Users should
instead use the `tff.learning.models` package for these symbols.
* Removed deprecated `tff.learning.federated_aggregate_keras_metric` function.
* Removed implicit attribute forwarding on
`tff.simulation.compose_dataset_computation_with_learning_process`.
* Removed deprecated `tff.framework.remote_executor_factory_from_stubs`.
* Removed deprecated `tff.backends.xla` APIs.
* Renamed the `tff.backends.test` APIs to:
`tff.backends.test.(create|set)_(sync|async)_test_cpp_execution_context`.