Documentation for #[inline] in the reference doesn't align with external resources

The current documentation for #[inline] places huge emphasis on its effect as an inlining hint. I was recently referred to the reference when I tried to inform another user that its primary effect is enabling cross-crate inlining of non-generic functions. I'm not sure if this lack of documentation is just an oversight (which I'm happy to correct with a PR) or if this is deliberate because the cross-crate inlining effect is planned to be removed, or if the hint is guaranteed, but the codegen difference isn't.

I'm particularly concerned, because this effect is well-known in resources outside of the reference:
https://matklad.github.io/2021/07/09/inline-in-rust.html
https://github.com/rust-lang/hashbrown/pull/119#issuecomment-537539046

Start with the Rust Reference entry for #[inline] and compare its wording with the two external resources linked in the issue. Clarify whether cross-crate inlining of non-generic functions is an intended effect and how the inlining hint is guaranteed. Done means the reference accurately documents the agreed behavior; confirm the wording with maintainers before editing.