Add support for Tensorflow SparseTensors: Dot merging layer.

[hertschuh]

Added tf.SparseTensor support for ops:

• matmul (sparse support was very partial before this PR)
• squeeze
• expand_dims

Added tf.SparseTensor support for merging layer:

• Dot

[codecov[bot]]

Codecov Report

Patch coverage: 94.91% and project coverage change: +0.01% :tada:

Comparison is base (bf04179) 83.80% compared to head (e33e1cf) 83.82%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #937 +/- ## ========================================== + Coverage 83.80% 83.82% +0.01% ========================================== Files 318 318 Lines 28780 28831 +51 Branches 5506 5518 +12 ========================================== + Hits 24120 24168 +48 - Misses 3145 3146 +1 - Partials 1515 1517 +2 ``` | [Flag](https://app.codecov.io/gh/keras-team/keras-core/pull/937/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/937/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | `83.71% <94.91%> (+0.01%)` | :arrow_up: | | [keras_core-jax](https://app.codecov.io/gh/keras-team/keras-core/pull/937/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | `66.98% <15.25%> (-0.11%)` | :arrow_down: | | [keras_core-numpy](https://app.codecov.io/gh/keras-team/keras-core/pull/937/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | `60.50% <15.25%> (-0.09%)` | :arrow_down: | | [keras_core-tensorflow](https://app.codecov.io/gh/keras-team/keras-core/pull/937/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | `66.95% <94.91%> (+0.04%)` | :arrow_up: | | [keras_core-torch](https://app.codecov.io/gh/keras-team/keras-core/pull/937/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | `69.05% <15.25%> (-0.11%)` | :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/937?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/backend/tensorflow/numpy.py](https://app.codecov.io/gh/keras-team/keras-core/pull/937?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team#diff-a2VyYXNfY29yZS9iYWNrZW5kL3RlbnNvcmZsb3cvbnVtcHkucHk=) | `93.93% <94.23%> (-0.03%)` | :arrow_down: | | [keras\_core/ops/numpy.py](https://app.codecov.io/gh/keras-team/keras-core/pull/937?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team#diff-a2VyYXNfY29yZS9vcHMvbnVtcHkucHk=) | `94.41% <100.00%> (+<0.01%)` | :arrow_up: |

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