Changes:
(1) Replaces the old dp_query `CentralTreeSumQuery` with the updated one `TreeRangeSumQuery`. The updated query has several advantages:
    1) It easily supports different DP mechanisms (e.g. GaussianSumQuery,
    DistributedDiscreteGaussianSumQuery) by taking them as inner queries;
    2) `TreeRangeSumQuery` does not hard-code any clipping inside so it is
    composable with various clipping factories. To avoid DP error, it does norm
   checking inside to make sure appropriate clipping happens outside.
(2) Removes the type conversion from int32 to float32 before return in `discretized_histogram_counts`. Now the function outputs int32 tensors. This change is due to the type requirement of `HistogramClippingSumFactory`.
(3) Updates tff's dependency on tensorflow privacy to 0.7.0.
PiperOrigin-RevId: 390277449