[c++] Don't use Python to generate C++ test inputs

[johnkerl]

Issue and/or context: Found in #1511 / #866 et al. while attempting pre-tag/pre-merge tests with core 2.17.0-rc0. Here we use tiledbsoma-py to generate test data for libtiledbsoma code. That's currently failing due to tiledbsoma-py in the generator step being built with core 2.16 rather than 2.17. But this highlights a bigger issue: let's not be circular in our test paths. Rather, let's validate C++ code using C++ and shell tools; then move up the testing stack to Python and R.

Changes: Simply can the generated inputs into test/soco.tgz. As an added bonus we get some backward-compatilbility test here.

Notes for Reviewer:

[codecov-commenter]

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