[CMake] Deprecate build.sh

`build.sh` has always been purely a wrapper around CMake. After community transition we have added a 'bare' CMake workflow that doesn't use it and now using that exclusively in CI. The script seems to only convert its non-sticky `--option`'s to CMake's normally-sticky `-DOPTION`'s, which requires additional logic in the main CMakeLists.txt.

We should also try to inventory what other options `build.sh` has and try to port them back to regular CMake if they are useful. I've recently found ccache which went into #7053.

This is low priority and shouldn't go to the release branch.

#1616 is also talking about improving CMake support.