Either deprecate macos support or test it in CI

[antoninbas]

The stuff in https://github.com/p4lang/behavioral-model/tree/main/tools/macos has not been updated (or I assume, tested) in years. We should either:

1. Add a disclaimer notice to that folder indicating that the scripts are not tested and unlikely to work on recent macOS versions without modification. We should also update the reference to these scripts in the README. It's the easy way out... Or,

2. Update the scripts and add new Github workflow using the macos runners to validate that dependencies can be installed and bmv2 can build successfully. This could be a lot of work, and be a significant maintenance effort moving forward.

[fruffy]

Option 2 would be nice since we do have good MacOS support for P4C. Part of the reason support is now easier for P4C is because we control most of the dependency versions with CMake's FetchContent. This reduces the amount of different dependency versions users can realistically have.

Iirc we do not have this with BMv2 other than using third-party for CI. Unclear how much maintenance work this would require.