Honor `avoid-breaking-exported-api` in `needless_pass_by_ref_mut`
Until now, the lint only emitted a warning, when breaking public API. Now it doesn't lint at all when the config value is not set to `false`, bringing it in line with the other lints using this config value.
Also ensures that this config value is documented in the lint.
changelog: none
(I don't think a changelog is necessary, since this lint is in `nursery`)
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Fixes https://github.com/rust-lang/rust-clippy/issues/11374
cc `@GuillaumeGomez`
Marking as draft: Does this lint even break public API? If I change a function signature from `fn foo(x: &mut T)` to `fn foo(x: &T)`, I can still call it with `foo(&mut x)`. The only "breaking" thing is that the `clippy::unnecessary_mut_passed` lint will complain that `&mut` at the callsite is not necessary, possibly trickling down to the crate user having to remote a `mut` from a variable. [Playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=058165a7663902e84af1d23e35c10d66).
Are there examples where this actually breaks public API, that I'm missing?
918ae1bec4