[c++] Resize for variant-indexed DataFrame

[johnkerl]

Issue and/or context: This follows on #2917 for issue #2407 / [sc-51048]. Here we implement resize.

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

Changes:

While SOMASparseNDArray and SOMADenseNDArray must always and only have int64 dims within the SOMA data model, SOMADataFrame is different. The default behavior -- which almost everyone uses -- has a single soma_joinid dim which is indeed of type int64. (Also note that exp.obs.shape does exist within TileDB-SOMA-Py, and people do call it.) However, the spec only requires that soma_joinid exist as a dim or an attr: it can be a dim along with others, or it can not be a dim at all. Here we do the right thing, without and with current-domain support, to allow people to resize the soma_joinid dim, and only that, whether it's the sole dimension, a dimension but not the sole one, or not a dim at all.

Notes for Reviewer:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.02%. Comparing base (f5ae258) to head (0c863d9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2917      +/-   ##
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+ Coverage   89.87%   90.02%   +0.15%     
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  Files          38       38              
  Lines        3999     3999              
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+ Hits         3594     3600       +6     
+ Misses        405      399       -6     

Flag	Coverage Δ
python	90.02% <ø> (+0.15%)	⬆️

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Components	Coverage Δ
python_api	90.02% <ø> (+0.15%)	⬆️
libtiledbsoma	∅ <ø> (∅)