`BUILD_TESTING` is a CMake provided option and we should use similar naming,
just like how Abseil does it.
- `SAPI_ENABLE_TESTS` -> `SAPI_BUILD_TESTING`
- `SAPI_ENABLE_CONTRIB_TESTS` -> `SAPI_CONTRIB_BUILD_TESTING`
- `SAPI_ENABLE_EXAMPLES` -> `SAPI_BUILD_EXAMPLES`
Drive-by:
- Fix option name in GitHub action
PiperOrigin-RevId: 443305932
Change-Id: Ice2b42be1229a0f9ae7c2ceda9ce87187baf22c4
Including the `CTest` modules ensures that the `BUILD_TESTING` option is
defined and automatically calls `enable_testing()` if needed. It does not
change the default or introduce any dependencies on its own.
This follows what Abseil already does in their top-level `CMakeLists.txt`.
PiperOrigin-RevId: 443305646
Change-Id: If067c17470f497437c7748aab4aab5227c26e84f
