FI-2981: Update matrix generation for deeply nested tests

[Jammjammjamm]

This branch updates the matrix generation to handle tests at different levels of nesting.

If you run bundle exec rake g10_test_kit:generate_matrix and examine the newly generated matrix, you should see:

• On the "Matrix" sheet, 9.14 should be identified as satisfying AUT-PAT-28.
• On the "Inferno Tests" sheet, all of the tests under 9.14 should appear.

This branch is on top of #537 because that PR contains the deeply nested tests which this change supports.