Roadmap to Sparse Array and deprecation of Sparse Matrix

I'd like to get feedback on a plan to move forward with the conversion to Sparse Arrays and the deprecation of Sparse Matrices. Let me know if there is a better way to do this. I could e.g. make a PR to the roadmap part of the docs if that's preferred. But this probably gets a larger audience, so I'll start here. I've discussed this with people working on sparse arrays, (special thanks to @stefan and @perimosocordiae ).


Roadmap
-------

Current work: 
- Provide a feature-complete sparse array api (including 1d-array and construction functions).
  - provide construction functions for sparse arrays <**very close**>
  - extend sparse array api to 1d arrays.
    - coo and dok formats <close but probs early v1.13dev>
    - some 1d format that uses 2d csr sparsetools to do 1d things: indexing/min-max/arithmetic. This could be built within the current 2d coo/csr classes or as a new format. <v1.13dev>

Next steps:
- Help other libraries convert to sparse arrays from sparse matrices.
    - networkx is already migrated
    - sklearn is [in progress 27090](https://github.com/scikit-learn/scikit-learn/issues/27090) 
    - scikit-image [preparation in 6261](https://github.com/scikit-image/scikit-image/pull/6261)
- wait for sparse array code to mature (1 cycle?)
- create deprecation guide, transition guide, helpful scripts to flag code for further examination.
- add deprecation warnings for sparse matrix.
- shift focus to numpy and deprecation/removal of numpy matrix.
- wait for requisite time after deprecation announced.
- remove sparse matrix
- start api shift of construction function names (`diags`, `block`, etc.)
    - Note: as a whole, the construction functions will undergo two name shifts. Once to move from matrix creation to new functions for array creation (i.e. `eye` -> `eye_array`). Then a second move to change names to match the array_api name (i.e. `eye_array` to `eye`) after sparse matrices are removed.
- add construction function names matching array_api names.
- deprecate the transition construction function names. 

Timeframe
---------
Steps with time impact:
1) feature-complete sparse array api
2) wait one release while helping other libraries convert to sparse array.
3) deprecation warnings for sparse matrix
4) wait requisite release cycles
5) remove sparse matrix code
6) work on function name shift deprecation process

One possible timing could be:
- scipy-1.13 feature-complete array api
- scipy-1.14 add deprecation warnings to matrix api
- scipy-1.16 remove matrix api
- scipy-1.17 deprecate for name changes
- scipy-1.19 complete name changes
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