Documentation: sorting impls for structs: first crate's own impls, then std impls

[rodrigocfd]

Problem

When we generate the documentation for a crate, all the crate implementations are sorted alphabetically. The crate's own traits and the std traits are all mixed together.

Proposed Solution

List first the crate's own traits, alphabetically. Then followed by std traits, alphabetically.

Notes

No response

[ehuss]

Transferred to rust-lang/rust. This behavior is controlled by rustdoc, and its issues are tracked here.