Add sparseness inference for TensorFlow backend ops and base layer.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.03% :warning:

Comparison is base (ac8a204) 76.45% compared to head (ea510e9) 76.43%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #878 +/- ## ========================================== - Coverage 76.45% 76.43% -0.03% ========================================== Files 329 329 Lines 31333 31331 -2 Branches 6100 6100 ========================================== - Hits 23955 23947 -8 - Misses 5799 5803 +4 - Partials 1579 1581 +2 ``` | [Flag](https://app.codecov.io/gh/keras-team/keras-core/pull/878/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | Coverage Δ | | |---|---|---| | [keras_core](https://app.codecov.io/gh/keras-team/keras-core/pull/878/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | `76.33% <100.00%> (-0.03%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files Changed](https://app.codecov.io/gh/keras-team/keras-core/pull/878?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | Coverage Δ | | |---|---|---| | [keras\_core/layers/core/identity.py](https://app.codecov.io/gh/keras-team/keras-core/pull/878?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team#diff-a2VyYXNfY29yZS9sYXllcnMvY29yZS9pZGVudGl0eS5weQ==) | `100.00% <ø> (ø)` | | | [keras\_core/backend/tensorflow/core.py](https://app.codecov.io/gh/keras-team/keras-core/pull/878?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team#diff-a2VyYXNfY29yZS9iYWNrZW5kL3RlbnNvcmZsb3cvY29yZS5weQ==) | `96.24% <100.00%> (+0.05%)` | :arrow_up: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/keras-team/keras-core/pull/878/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team)

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