Clarify M-SMALLER-CRATES is mostly orthogonal to whether users should see the smaller crates.

... in other words, it's perfectly normal in rust to have `foo` re-exporting `foo_x` and `foo_y` as an umbrella, and rightfully expecting that users will not deal with `foo_x` and `foo_y` directly (and if they do and run into issues, e.g., around macros) it's just a not supported use case).

Locate the guideline section discussing M-SMALLER-CRATES and read its surrounding guidance on crate visibility and re-exports. Clarify that the guideline is independent of whether users should interact with smaller crates, while preserving the umbrella-crate example. Done when the resulting wording states this distinction unambiguously; no test is mentioned.

Written by the indexing model from the issue text.