[c++] General CMake clean-up

[jp-dark]

Issue and/or context: Closes #2664

Changes:

• Add options explicitly to targets instead of to everything. Note: this means compile options are no longer propagated to third-party libraries included with FetchContent and ExternalProject_Add.
• Move find_package calls and coverage flags to base CMakeLists.txt instead of adding them twice.
• Re-arrange some CMake calls to reduce redundancy and improve readability.
• Remove unused GIT_COMMIT_HASH compiler definition.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 90.02%. Comparing base (9cfbdca) to head (b47cee7).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2762 +/- ## ========================================== + Coverage 89.87% 90.02% +0.15% ========================================== Files 37 37 Lines 3939 3939 ========================================== + Hits 3540 3546 +6 + Misses 399 393 -6 ``` | [Flag](https://app.codecov.io/gh/single-cell-data/TileDB-SOMA/pull/2762/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=single-cell-data) | Coverage Δ | | |---|---|---| | [python](https://app.codecov.io/gh/single-cell-data/TileDB-SOMA/pull/2762/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=single-cell-data) | `90.02% <ø> (+0.15%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=single-cell-data#carryforward-flags-in-the-pull-request-comment) to find out more. | [Components](https://app.codecov.io/gh/single-cell-data/TileDB-SOMA/pull/2762/components?src=pr&el=components&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=single-cell-data) | Coverage Δ | | |---|---|---| | [python_api](https://app.codecov.io/gh/single-cell-data/TileDB-SOMA/pull/2762/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=single-cell-data) | `90.02% <ø> (+0.15%)` | :arrow_up: | | [libtiledbsoma](https://app.codecov.io/gh/single-cell-data/TileDB-SOMA/pull/2762/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=single-cell-data) | `∅ <ø> (∅)` | |