…llaumeGomez

Rollup of 10 pull requests

Successful merges:

 - rust-lang#119888 (Stabilize the `#[diagnostic]` namespace and `#[diagnostic::on_unimplemented]` attribute)
 - rust-lang#121089 (Remove `feed_local_def_id`)
 - rust-lang#122004 (AST validation: Improve handling of inherent impls nested within functions and anon consts)
 - rust-lang#122087 (Add missing background color for top-level rust documentation page and increase contrast by setting text color to black)
 - rust-lang#122136 (Include all library files in artifact summary on CI)
 - rust-lang#122137 (Don't pass a break scope to `Builder::break_for_else`)
 - rust-lang#122138 (Record mtime in bootstrap's LLVM linker script)
 - rust-lang#122141 (sync (try_)instantiate_mir_and_normalize_erasing_regions implementation)
 - rust-lang#122142 (cleanup rustc_infer)
 - rust-lang#122147 (Make `std::os::unix::ucred` module private)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of rust-lang#122147 - kadiwa4:private_impl_mods, r=workingjubilee

Make `std::os::unix::ucred` module private

Tracking issue: rust-lang#42839

Currently, this unstable module exists: [`std::os::unix::ucred`](https://doc.rust-lang.org/stable/std/os/unix/ucred/index.html).
All it does is provide `UCred` (which is also available from `std::os::unix::net`), `impl_*` (which is probably a mishap and should be private) and `peer_cred` (which is undocumented but has a documented counterpart at `std::os::unix::net::UnixStream::peer_cred`).

This PR makes the entire `ucred` module private and moves it into `net`, because that's where it is used.

I hope it's fine to simply remove it without a deprecation phase. Otherwise, I can add back a deprecated reexport module `std::os::unix::ucred`.

`@rustbot` label: -T-libs +T-libs-api