[python] Centralize sparse/dense pybind11 shape methods

[johnkerl]

Issue and/or context: As tracked on issue #2407 / [sc-51048].

Note that the intended Python and R API changes are all agreed on and finalized as described in #2407.

Changes:

This is a split-out to simplify #3244 which turns out to be multi-faceted

Notes for Reviewer:

No new unit tests -- proof of success here is that all existing unit-test cases contiunue to pass.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 83.91%. Comparing base (467af01) to head (88ee4e8).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3261      +/-   ##
==========================================
+ Coverage   83.79%   83.91%   +0.11%     
==========================================
  Files          51       51              
  Lines        5560     5563       +3     
==========================================
+ Hits         4659     4668       +9     
+ Misses        901      895       -6     

Flag	Coverage Δ
python	83.91% <75.00%> (+0.11%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
python_api	83.91% <75.00%> (+0.11%)	⬆️
libtiledbsoma	∅ <ø> (∅)

[nguyenv]

lgtm