[Feature Request][move-compiler-v2] add an attribute to include #[test_only] functions in coverage

[brmataptos]

🚀 Feature Request

@alnoki asks:

Is there a way to enforce coverage testing on functions like these if I make them [#test_only]? I made them private fun without #[test_only] because I needed to verify that I had tested every invariant failure method (via the coverage tool, but I don’t actually need the fun verify and fun verify_subtree bytecode in production: perhaps a directive like #[test_only, include_in_coverage]?

This seems feasible.

[alnoki]

@brmataptos thanks for filing this! For reference here are the functions I'm currently using for fuzzing: https://github.com/econia-labs/econia-v5/blob/b62a697b169adfbe3db05d9c84bb21681134aa67/src/move/research/red-black-map/variants/b/sources/red_black_map.move#L387-L408