primitive docs should show core/alloc/std accessibility #62909
Description
In #61851, I tried to generate primitive docs in core, similar to those in std. My main motivation was to clearly see what f64 methods are available in core alone, under #[no_std], since a lot of them require std and libm support. However, I had trouble making that work because of broken documentation links between core and std-specific methods.
So I think instead, rustdoc could put some kind of marker on primitive methods to indicate what crate added them, so the accessibility is known. Apart from floating point, there are also a few slice methods that are only added in alloc. Maybe there are more that I don't know yet!